A. "on" is used when a specific date or day is mentioned. For example, "on Saturday".
B. "in" is used with a specific period of time. For example, in a year, in a week, etc.
C. "for" is used when a specific time period is mentioned. For example, "for a year" D. "since" is the correct answer as it is used with the starting of a particular period. For example, since last summer, since yesterday.