A.I. Explanation:

Correct answer: both

Explanation: The word 'both' correctly indicates that two elements, temperature and speed of sound, are decreasing together. This fits grammatically as it aligns with the plural subject and contextually emphasizes the simultaneous decrease of both factors as altitude increases.

Meaning: 'Both' refers to two items or elements together, in this case, temperature and speed of sound.

Wrong options:

• not: 'Not' negates a statement but does not convey the idea of two elements decreasing together, making it contextually inappropriate here.
• yet: 'Yet' implies contrast or exception, which does not fit the context of both elements decreasing as altitude increases.
• none: 'None' suggests the absence of something, which contradicts the idea that both temperature and speed of sound are indeed decreasing.

Correct answer: remains

Explanation: The word 'remains' is the correct choice as it indicates that the temperature stays constant after the initial decrease. It fits grammatically as a verb in the present tense and contextually describes the stability of temperature at higher altitudes.

Meaning: 'Remains' means to stay the same or continue to exist without change.

Wrong options:

• opposes: 'Opposes' suggests resistance or contradiction, which does not apply to the context of temperature staying steady.
• plots: 'Plots' refers to mapping or planning, which is irrelevant in this context where we discuss temperature stability.
• mutates: 'Mutates' implies a change or transformation, which contradicts the idea of temperature remaining steady.

Correct answer: variation

Explanation: The word 'variation' is appropriate as it refers to the differences in temperature and speed of sound at different altitudes. It fits grammatically as a noun and contextually highlights the changes that allow for the described phenomenon.

Meaning: 'Variation' means a change or difference in condition, amount, or level, which is relevant to the context of altitude affecting sound speed.

Wrong options:

• variety: 'Variety' refers to different types or kinds, which does not accurately describe the changes in temperature and speed of sound.
• ventilation: 'Ventilation' relates to air circulation, which is not relevant to the context of sound speed and temperature changes.
• similarity: 'Similarity' indicates likeness, which contradicts the idea of change or difference that 'variation' conveys.

Correct answer: from

Explanation: The word 'from' correctly indicates the starting point of the transonic band, aligning with the context of describing a range. It fits grammatically as a preposition and contextually establishes the range of Mach values.

Meaning: 'From' indicates the starting point of a range or distance, in this case, the beginning of the transonic band.

Wrong options:

• near: 'Near' suggests proximity but does not indicate a starting point, making it contextually inappropriate here.
• with: 'With' implies accompaniment, which does not fit the context of defining a range starting at Mach 0.8.
• in: 'In' suggests inclusion within a space, which does not accurately describe the starting point of the transonic band.

Correct answer: form on

Explanation: The phrase 'form on' is correct as it describes the creation of shock waves on the wing. It fits grammatically as a verb phrase and contextually conveys the action of shock waves developing at a specific point.

Meaning: 'Form on' means to create or develop on a surface, in this case, the wing of the airplane.

Wrong options:

• diverge from: 'Diverge from' implies moving away from a point, which does not accurately describe the action of shock waves forming on the wing.
• add to: 'Add to' suggests increasing or contributing, which does not fit the context of shock waves forming.
• prevent from: 'Prevent from' indicates stopping something from happening, which contradicts the idea of shock waves forming.