根据句意，选用适当的词填空。

1. —Is this your pencil?

    —No,it isn't. ______ (That,That's) my pencil.

2. —What's this?

    —______(It's, Its) a red pen.

3. I can see______ (a, an) English girl.

4. —______(What's, What)color is the clock?

    —It's white.

5. —Excuse ______ (I, me),Sally. Is this your book?   

    —No, it isn't.