Meaning: A 'keystroke' is the action of pressing a key on a keyboard, often used in discussions about typing speed or computer input.

Wrong options:

• task: The word 'task' refers to a piece of work or duty, which does not specifically relate to the action of typing and thus does not fit the context of measuring time per action.
• control: 'Control' implies managing or directing something, which is not relevant to the context of measuring typing speed or actions.
• work: While 'work' can refer to effort or tasks performed, it is too broad and does not specifically relate to the singular action of typing a key.

Correct answer: emerged

Explanation: The verb 'emerged' is correctly used in the past participle form, indicating the beginning of life within a specified time frame. It fits grammatically and contextually, as it refers to the origin of life on Earth.

Meaning: To 'emerge' means to come into existence or to become visible, particularly in the context of life beginning on Earth.

Wrong options:

• been extinct: 'Been extinct' is grammatically incorrect in this context as it suggests a state rather than the action of life beginning.
• died out: 'Died out' implies a cessation of existence, which does not fit the context of life beginning within a time frame.
• diverged: 'Diverged' suggests a branching off from a common point, which does not relate to the emergence of life.

Correct answer: phrase

Explanation: The word 'phrase' is a noun that refers to a small group of words that form a meaningful unit. It fits grammatically and contextually as it relates to the specific text being typed, making it the most appropriate choice.

Meaning: A 'phrase' is a sequence of words that convey a particular meaning, often used in writing or speech.

Wrong options:

• language: 'Language' refers to a system of communication, which is too broad and does not specifically relate to the act of typing a specific set of words.
• number: 'Number' refers to a numerical value, which does not fit the context of typing a specific text or statement.
• alphabet: 'Alphabet' refers to a set of letters or symbols used in writing, which is not relevant to the specific action of typing a particular phrase.

Correct answer: string

Explanation: The term 'string' is used correctly as a noun that refers to a sequence of characters or data, fitting well in the context of DNA, which is often described in terms of its sequence. It aligns grammatically and contextually with the sentence.

Meaning: A 'string' in this context refers to a sequence of characters or elements, particularly in relation to DNA sequences.

Wrong options:

• sting: 'Sting' refers to a sharp pain or a type of injury, which does not relate to the context of DNA or sequences.
• spot: 'Spot' refers to a mark or location, which is not relevant to the context of DNA structure or sequences.
• point: 'Point' can refer to a specific location or detail, but it does not accurately describe the concept of a sequence in DNA.