Explanation:

Definition:
A leap year is a year that is exactly divisible by 4, except for years that are divisible by 100. However, years that are divisible by 400 are leap years.

Analysis:
Let's analyze each given option to determine if it is a leap year or not:

a) 700:
To check if 700 is a leap year, we need to determine if it is divisible by 4. If it is divisible by 4, it could be a leap year. However, 700 divided by 4 is 175, which is not an integer. Therefore, 700 is not a leap year.

b) 2000:
To check if 2000 is a leap year, we need to apply the rules stated above.
- 2000 is divisible by 4, which satisfies the first condition.
- 2000 is also divisible by 100, but since it is also divisible by 400, it satisfies the exception rule.
Therefore, 2000 is a leap year.

c) 900:
To check if 900 is a leap year, we need to determine if it is divisible by 4. If it is divisible by 4, it could be a leap year. However, 900 divided by 4 is 225, which is not an integer. Therefore, 900 is not a leap year.

d) 1000:
To check if 1000 is a leap year, we need to determine if it is divisible by 4. If it is divisible by 4, it could be a leap year. However, 1000 divided by 4 is 250, which is not an integer. Therefore, 1000 is not a leap year.

Conclusion:
Out of the given options, only option 'b' (2000) is a leap year according to the rules defined.