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】复合句。句首为 because 引导的原因状语从句。主句的主干为 a good laugh is unlikely to have measurable benefits，主句包含 the way 引导的方式状语从句，say 作插入语。

【译文】但是，由于“大笑”很难持续，一场酣畅淋漓的大笑给心血管带来的好处，不可能会像散步和慢跑给心血管带来的好处那样明显可见。

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】复合句。句首 It 为形式主语，真正的主语为 that 引导的从句。从句由 but 连接的并列复合句构成，第一个分句包含 because 引导的原因状语从句，第二个分句包含 when 引导的时间状语从句。

【译文】19世纪末曾有人提到：人类不是因为悲伤而哭泣，而是因为流泪而悲伤。