Susan came . . . . . . . . three days. A. on B. in C. at D. after

The correct answer is A. on.

The preposition “on” is used to indicate a specific day or date. In this case, the sentence is saying that Susan came on three days. This could mean that she came on three separate days, or that she came for three days in a row.

The other options are not as accurate. The preposition “in” is used to indicate a period of time, not a specific day. The preposition “at” is used to indicate a specific time, not a specific day. The preposition “after” is used to indicate a time that comes after another time.

Here are some examples of how the preposition “on” can be used:

• Susan came on Tuesday.
• Susan came on the 1st of January.
• Susan came on the weekend.
• Susan came on my birthday.

Here are some examples of how the preposition “in” can be used:

• Susan came in the morning.
• Susan came in the afternoon.
• Susan came in the evening.
• Susan came in the summer.

Here are some examples of how the preposition “at” can be used:

• Susan came at 10:00 AM.
• Susan came at noon.
• Susan came at 5:00 PM.
• Susan came at midnight.

Here are some examples of how the preposition “after” can be used:

• Susan came after I left.
• Susan came after dinner.
• Susan came after the movie.
• Susan came after the party.