When/Why is your birthday?

Solution:

The question "When/Why is your birthday?" asks for the date or reason of a birthday. Looking at the options:

1. Option 'a' "Valentine's Day!" is a holiday, not a birthday.
2. Option 'b' "It's on 16th June." provides a specific date, which can answer "When is your birthday?".
3. Option 'c' "By bus." is a mode of transportation.
4. Option 'd' "Because I lost my new watch." is a reason for sadness.
5. Option 'e' "They're fairy penguins." describes beings.
6. Option 'f' "We can!" is a statement of ability.
7. Option 'g' "It's in the cupboard." is a location.

Therefore, the answer that specifies a date for the birthday is "It's on 16th June." This corresponds to option 'b'.

Answer: b It's on 16th June.