Analysis:
The sentence describes Sam's lateness as something that irritates the speaker. The idiom 'gets on my nerves' means to annoy or irritate someone.
Breakdown:
- A to: Incorrect. 'Gets to my nerves' is not the correct idiom.
- B on: Correct. 'Gets on my nerves' is the standard idiom for annoyance.
- C at: Incorrect. 'Gets at my nerves' is not the correct idiom.
Translated Question:
21 Сэм всегда опаздывает. Это действует мне ..... нервы.