1.句子主干是“我们走回家”，两个句子是因果关系。半小时过去了所以用过去式。句子中要用到go by，半小时过去了应翻译成half an hour gone by
Half an hour gone by，but the last bus had not come so we had to go home on foot.
2.句子主干是“玛丽对汉语考试很担心”，两个句子是因果关系用连词because连接两个句子，时态用一般现在时，看上去用look，背熟课文用learn the text by heart
Mary looks very worried about the Chinese exam because she has not learned the text by heart.
3.句子主干是“我们去参观博物馆”，前后是因果关系，since引导原因状语从句，在这里是既然的意思，主句用一般现在时，从句现在完成时，推迟用“postpone”。
Since the basketball match has been postponed we may as wall visit the museum.
4.句子主干是“他住在澳大利亚”，动作已经完成，用现在完成时，一直用“all the way”时间放在句前，地点放在句末。
Entire world war II period he has been living with his parents all the way in Australia.
5.句子主干是“我与我的大学同学失去了联系”，since引导时间状语从句，主句用现在完成时，从句用一般过去时，失去联系用lose touch 可以说用kind of
Since I graduated from Nanjing university in 1985，I have kind of lost touch with my classmates.
