选词填空。
1. The birds are ________________ ( sing , singing ).
2. Are these mom’s ________________ ( sock , socks ) ? I don’t know.
3. Is that __________ ( your , yours ) coat ? No, it’s not __________ ( my , mine ).
4. _________ ( Our , Ours ) shoes are blue. _________ ( Their, Theirs ) are brown.
5. Tony wants _____________ ( be , to be ) a firefighter.
6. The writers _____________ ( have , has ) ten red balloons.