一、同义句转换

前两题正确：should do sth = be supposed to do sth，意思是“应该/应当做某事”。

但是后两题不对，be supposed to do sth没有be allowed to do sth或can do sth的意思。

可以分别改成：

3. are forbidden to

4. aren't allowed/permitted to 或 are forbidden to 或 mustn't

二、翻译句子

1. first time有误，应该改成：for the first time

2. 正确

3. 错误，主语搞笑了，呵呵（介词短语不能做句子主语），可以写成：

Playing football isn't allowed in the classroom.

4. an hour ago不对，ago一般只用于一般过去时。可以改成：

They are supposed to arrive/get/reach here an hour ahead/earlier.

或：They are supposed to have arrived here an hour ahead/earlier.