Select the most appropriate option to fill in the blank.

The Mid-Day Meal Programme has been running ______ 21 years.

for

The most appropriate option to fill in the blank is: for

The sentence should be: "The Mid-Day Meal Programme has been running for 21 years."

Explanation:
- "For" is used to indicate a period of time during which something has been happening or in existence. In this case, it indicates the duration of 21 years for which the Mid-Day Meal Programme has been running.

• "For" indicates a duration of time. In this context, we want to express how long the program has been running.
• "Off" suggests a cancellation or stopping of something, which isn't the case here.
• "Since" can also be used to indicate a starting point in time, but "for" is more natural for expressing duration.
• "Of" doesn't typically connect to timeframes in this way.