基本句子结构：
S + LV + A （主语 + 系动词 + 形容词）

1. The number of visitors to U.S.A. ________________________ during the summer.
到美国的游客的数目在夏季保持不变。

2. Cloning is _____________________________.
克隆技术是违背自然和不道德的。

3. He Guofang is ____________________________.
何国方有才华且为人谦逊。

4. The proposal that women should go back home to be full-time¹ housewives seems ______________________.
妇女应该回家做全职太太的建议似乎不切实际并很荒唐。

答案：
1.remained constant
2.unnatural² and not ethically³ correct
3.talented and modest
4.impractical and ridiculous