Leap year is the one which is divisible by 4. Every fourth year is a leap year.

Explanation:
A leap year is a year that has one additional day, February 29th, making it a total of 366 days instead of the usual 365 days. Leap years are necessary to keep our calendar in alignment with the Earth's revolutions around the sun.

Identifying a Leap Year:
To determine if a year is a leap year, we need to follow a set of rules. These rules are as follows:

1. A year that is divisible by 4 is a leap year.
2. However, a year that is divisible by 100 is not a leap year, except if it is divisible by 400.

Analysis of Options:
Let's analyze the given options to identify if they are leap years or not:

a) 1980:
- 1980 is divisible by 4, so it meets the first rule.
- 1980 is not divisible by 100, so it does not meet the second rule.
- Therefore, 1980 is a leap year.

b) 1981:
- 1981 is not divisible by 4, so it does not meet the first rule.
- Therefore, 1981 is not a leap year.

c) 1982:
- 1982 is not divisible by 4, so it does not meet the first rule.
- Therefore, 1982 is not a leap year.

d) All of these:
- Since options b) and c) are not leap years, "All of these" cannot be the correct answer.

Conclusion:
Based on the analysis above, option a) 1980 is the only leap year among the given options.