【正文】
at 從句才是真正的主語(yǔ)。例如: It’s pleasant to meet old friends here. 在這兒遇見(jiàn)老朋友真讓人高興。其中 for 引出動(dòng)詞不定式的邏輯主語(yǔ),指明我們說(shuō)的是誰(shuí)。 Key: 1. It is polite that students often give seats to the elderly on the bus. 2. It is impossible to finish all the homework in an hour. 3. It is dangerous for her to go swimming alone. 4. It is tough to walk a 100kilometre trail within 48 hou