治疗免疫性不孕,应首选( )。
What item is mainly assessed in the following question?
How well did you work in your group tasks?
一般来说,声音不是商品,但是一些商家把大自然中的鸟语、虫鸣和小溪的潺潺水声录下并加以剪辑制成磁带出售,这些具有自然之声的磁带就成了商品。这是因为( )。