A:had put; might not have bee
B:had put; could be
C:had put; might be
D:had not put; could not have bee
一长为L、质量m且分布均匀的细绳平放在水平地面上,把这根细绳从一端缓慢提起.当这根绳的末端刚离地面时,绳子的重力势能增加 ____.
下列现象发生在人体呼气过程中的是( )