Question

2．瑪麗在七歲時會騎自行車．（could，when ）
Mary could swim when she was five．

Answer 1

分析 Mary could swim when she was five．

解答 答案：Mary could swim when she was five．
表達(dá)的是過去的事情用一般過去時，表示能做某事用情態(tài)動詞can的過去式could，后加動詞原形swim，故Mary could swim．when引導(dǎo)的時間狀語從句，主語she，故was，故答案是Mary could swim when she was five．

點評 when引導(dǎo)時間從句用過去時，主句用過去進(jìn)行時：表示在從句動作在過去發(fā)生時，主句的動作在當(dāng)時也正在進(jìn)行．用于表示在過去有兩個動作同時發(fā)生的情況，或者一前一后即在過去某動作發(fā)生時或正在進(jìn)行中，又有一個動作發(fā)生的情況（反之亦然），通常短暫性動詞用過去時，持續(xù)性動詞用過去進(jìn)行時．
When I got up，my mum was serving breakfast．
When I was having breakfast，my dad went out of home．