Meaning: 'Stretches' means to extend over a certain distance.

Wrong options:

• stay: 'Stay' is a verb that means to remain in a place, which does not convey the idea of length or distance.
• created: 'Created' is in the past tense and does not fit the context of describing the current state of the Great Wall.
• balance: 'Balance' is a noun or verb that refers to stability or equilibrium, which is unrelated to the physical extent of the Great Wall.

Correct answer: ancient

Explanation: 'Ancient' is an adjective that describes something very old, fitting perfectly in the context of the historical silk route.

Meaning: 'Ancient' refers to something that has existed for a very long time, often associated with history.

Wrong options:

• stay: 'Stay' is a verb that does not describe the nature of the silk route and is grammatically incorrect here.
• scratch: 'Scratch' is a noun or verb that refers to a mark or the act of scraping, which does not relate to the silk route.
• balance: 'Balance' does not fit contextually as it does not describe the silk route and is unrelated to its historical significance.

Correct answer: raiding

Explanation: 'Raiding' is a gerund that describes the action of attacking or plundering, which fits the context of the Hsiung-nu's activities against the emperor's land.

Meaning: 'Raiding' refers to the act of making a sudden attack in order to steal or cause damage.

Wrong options:

• stay: 'Stay' does not convey any action related to attacking and is grammatically incorrect in this context.
• created: 'Created' is in the past tense and does not fit the context of ongoing actions like raiding.
• balance: 'Balance' does not relate to the context of conflict or attack and is not appropriate here.

Correct answer: scratch

Explanation: 'Scratch' is a noun that refers to the starting point or beginning of something, fitting the context of not having to start building the wall from nothing.

Meaning: 'Scratch' means the starting point or the very beginning of a process.

Wrong options:

• stay: 'Stay' does not relate to the concept of starting a project and is grammatically incorrect here.
• raiding: 'Raiding' refers to an action of attack, which does not fit the context of beginning construction.
• balance: 'Balance' does not relate to the concept of starting from a point and is not appropriate in this context.

Correct answer: constructing

Explanation: 'Constructing' is a gerund that describes the ongoing action of building, which fits the context of the emperor's successors continuing the work on the wall.

Meaning: 'Constructing' means the act of building or making something.

Wrong options:

• stay: 'Stay' does not convey any action related to building and is grammatically incorrect in this context.
• created: 'Created' is in the past tense and does not fit the context of ongoing construction.
• balance: 'Balance' does not relate to the act of building and is not appropriate here.