按要求改写下列句子，一空一词，含缩略词。
Jack has an eraser in his pencil case.（改为一般疑问）
Jack              an eraser in his pencil case?
I think tennis is very interesting. （改为否定句）
I                              tennis is very interesting.
Her books are on the sofa.（对划线部分提问）
             are               books?
There are old bikes under the tree.（变为单数句）
There                                  old bike under the tree.
打乒乓球对我来说很简单。（完成译旬）
Playing ping-pong is                                  me．