Select the most appropriate homonym.
The guards will watch over the premises.

Correct option is B

The correct meaning of the underlined homonym ‘watch (over)’ in the sentence is ‘protect/guard’ (रक्षा करना/पहरेदारी करना). “Watch over” is a phrasal verb meaning to keep guard and ensure safety of someone/something—exactly what guards do for premises.
Example: At night, security personnel watch over the museum to protect the artifacts.
Meanings of the other options (and why incorrect):
• Timepiece (घड़ी): the noun watch meaning a small clock worn on the wrist; not the sense used here.
• Warn (चेतावनी देना): to alert of danger; “watch over” does not mean “warn.”
• Observe (देखना/निरीक्षण करना): to look carefully; weaker than the protective sense implied by watch over.