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.