Meaning: 'Efficient' means achieving maximum productivity with minimum wasted effort or expense.

Wrong options:

• manage: The word 'manage' is a verb that does not fit grammatically as it cannot describe 'means' in this context.
• traversing: 'Traversing' is a gerund that refers to the act of traveling, which does not describe the means of transport.
• earlier: 'Earlier' is an adjective that refers to time, which does not apply to the description of a means of transport.
• materials: 'Materials' is a noun that does not fit as it does not describe the effectiveness of the means of transport.
• accidental: 'Accidental' is an adjective that describes something happening by chance, which does not relate to the efficiency of transport.
• remote: 'Remote' is an adjective that describes distance, which does not apply to the effectiveness of the means of transport.
• matter: 'Matter' is a noun that refers to substance, which does not fit the context of describing a means of transport.

Correct answer: traversing

Explanation: The term 'traversing' is a gerund that refers to the act of traveling across or through something. It fits grammatically as it serves as the object of the preposition 'of' and contextually as it describes the action taken by people in the air.

Meaning: 'Traversing' means to travel across or through an area.

Wrong options:

• manage: 'Manage' is a verb that does not fit as it does not describe the action of traveling in the air.
• efficient: 'Efficient' is an adjective that does not fit as it does not describe an action but rather a quality.
• earlier: 'Earlier' is an adjective that refers to time and does not relate to the action of traveling.
• materials: 'Materials' is a noun that does not fit as it does not describe the action of traveling in the air.
• accidental: 'Accidental' is an adjective that does not describe an action and is irrelevant in this context.
• remote: 'Remote' is an adjective that describes distance and does not relate to the action of traveling.
• matter: 'Matter' is a noun that does not fit as it does not describe the action of traversing.

Correct answer: materials

Explanation: The word 'materials' is a plural noun that refers to the substances used to construct hot air balloons. It fits grammatically as the subject of the sentence and contextually as it describes what was used in the construction of the balloons.

Meaning: 'Materials' refers to the substances or components used to make something.

Wrong options:

• manage: 'Manage' is a verb that does not fit as it does not refer to substances used in construction.
• efficient: 'Efficient' is an adjective that does not fit as it does not describe substances.
• traversing: 'Traversing' is a gerund that refers to the act of traveling, which does not relate to the substances used.
• earlier: 'Earlier' is an adjective that refers to time and does not apply to the context of materials.
• accidental: 'Accidental' is an adjective that describes something happening by chance, which does not relate to the substances used.
• remote: 'Remote' is an adjective that describes distance and does not apply to materials.
• matter: 'Matter' is a noun that refers to substance but does not fit the context of describing the materials used.

Correct answer: accidental

Explanation: The term 'accidental' is an adjective that describes the discovery of hot air balloons as happening by chance. It fits grammatically as it modifies the noun 'discovery' and contextually as it reflects the unexpected nature of the invention.

Meaning: 'Accidental' means happening by chance or unexpectedly.

Wrong options:

• manage: 'Manage' is a verb that does not fit as it does not describe the nature of a discovery.
• efficient: 'Efficient' is an adjective that does not fit as it does not describe the nature of the discovery.
• traversing: 'Traversing' is a gerund that refers to the act of traveling, which does not relate to the nature of a discovery.
• materials: 'Materials' is a noun that does not fit as it does not describe the nature of a discovery.
• earlier: 'Earlier' is an adjective that refers to time and does not apply to the nature of a discovery.
• remote: 'Remote' is an adjective that describes distance and does not relate to the nature of a discovery.
• matter: 'Matter' is a noun that does not fit as it does not describe the nature of a discovery.

Correct answer: remote

Explanation: The word 'remote' is an adjective that describes areas that are far away or isolated. It fits grammatically as it modifies the noun 'areas' and contextually as it indicates locations where hot air balloons are still used due to lack of roads.

Meaning: 'Remote' means situated far from the main centers of population; distant.

Wrong options:

• manage: 'Manage' is a verb that does not fit as it does not describe the type of areas.
• efficient: 'Efficient' is an adjective that does not fit as it does not describe the type of areas.
• traversing: 'Traversing' is a gerund that refers to the act of traveling, which does not relate to the type of areas.
• materials: 'Materials' is a noun that does not fit as it does not describe the type of areas.
• accidental: 'Accidental' is an adjective that describes something happening by chance, which does not relate to the type of areas.
• earlier: 'Earlier' is an adjective that refers to time and does not apply to the type of areas.
• matter: 'Matter' is a noun that does not fit as it does not describe the type of areas.