সঠিক উত্তর: গ) on.
Complete sentence: The metro rail is running on time.
On-time:
English meaning: at the expected or scheduled time./ used to describe something that arrives, happens, or is done when it should and is not late.
Example: The airline ranked last in on-time arrivals last month.
Options,
We use at:
• with particular points on the clock:
Example: I’ll see you at five o’clock.
• with particular points in the day:
Example: The helicopter took off at midday and headed for the island.
• with particular points in the week:
Example: What are you doing at the weekend?
• with special celebrations:
Example: At the New Year, millions of people travel home to be with their families (but we say on your birthday).
-------------
We use on:
• with dates:
Example: We moved into this house on 25 October 1987.
• with a singular day of the week to refer to one occasion:
Example: I’ve got to go to London on Friday.
• with a plural day of the week to refer to repeated events:
Example: The office is closed on Fridays.
• with special dates:
Example: What do you normally do on your birthday?
---------------
We use in:
• with parts of the day:
Example: I’ll come and see you in the morning for a cup of coffee, okay?
• with months:
Example: We usually go camping in July or August.
• with years:
Example: The house was built in 1835.
• with seasons:
Example: The garden is wonderful in the spring when all the flowers come out.
• with long periods of time:
Example: The population of Europe doubled in the nineteenth century.
Source: Cambridge Dictionary.