1. What day is your birthday?

- It is June 14th.
- It is the second Monday.

2. When is your birthday?
- It's this Friday.
- It is on January 10th.
- It is January 10th.

3. What date is your birthday?
- It is January 10th.
- It is on January 10th.
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Are the questions and answers gramatical? Which ones are not suitable?

They are all correct and suitable.

The questions and answers provided are grammatically correct. However, some of the answers may not be suitable depending on the context. Let's analyze each question and answer:

1. What day is your birthday?
- It is June 14th. (Suitable)
- It is the second Monday. (Suitable, especially if the question is referring to a recurring date like "second Monday of every month.")

2. When is your birthday?
- It's this Friday. (Suitable if the current day is close to the mentioned Friday)
- It is on January 10th. (Suitable)
- It is January 10th. (Suitable)

3. What date is your birthday?
- It is January 10th. (Suitable)
- It is on January 10th. (Suitable)

In general, all the answers provided are suitable and grammatically correct for answering questions about someone's birthday.