2. But because hard laughter is diffficult to sustain, a good laugh is unlikely to have measurable benefits the way, say, walking or jogging does.

【分析】復合句。句首為 because 引導的原因狀語從句。主句的主干為 a good laugh is unlikely to have measurable benefits，主句包含 the way 引導的方式狀語從句，say 作插入語。

【譯文】但是，由于“大笑”很難持續，一場酣暢淋漓的大笑給心血管帶來的好處，不可能會像散步和慢跑給心血管帶來的好處那樣明顯可見。

3. It was argued at the end of the 19th century that humans do not cry because they are sad but they become sad when the tears begin to flow.

【分析】復合句。句首 It 為形式主語，真正的主語為 that 引導的從句。從句由 but 連接的并列復合句構成，第一個分句包含 because 引導的原因狀語從句，第二個分句包含 when 引導的時間狀語從句。

【譯文】19世紀末曾有人提到：人類不是因為悲傷而哭泣，而是因為流淚而悲傷。