句型转换。

1. This store sells school things. (改为否定句)

    This store_____ _____ school things.

2. They sell the books to me. (改为同义句)

    I _____ the books _____ them.

金属材料在无限多次交变载荷作用下，而不致裂的最大应力称为疲劳强度。