在Rt△ABC中，∠C=90°，若∠B=60°，b=30，则a+c=______．

要求进行句型转换，每空一词。

1. Those are pictures.   (改为单数句)

That's ______ _______.

2. This is an apple tree.  (改为复数句)

These _____ _____ ____.

3. There are some pictures on the wall.   (变为一般疑问句)

______ ______ _____ pictures on the wall?

4. There are some dictionaries in the library.  (变为否定句)

There _____ ______ dictionaries in the library.

5. There is a computer in the classroom.   There are two blackboards in the classroom.(把两句合为一句)

___________________________________.