用所给单词的适当形式填空
1. It ____(be) six thirty in the morning now.
The Smiths ____ (be) always ____(have)breakfast at this time.
2. –What ____ Mary ____ (do) on Sunday mornings?
-She often ____ (clean) her room.
通过对胎儿或新生儿的体细胞组织切片观察难以发现的遗传病是（ ）
孙中山认为，西方国家贫富不均，劳资矛盾尖锐，因此他提出民生主义，其实质目的是
