a. When there is a slight improvement in their children's studies, parents will feel happy. (请用名词词组替换when引导的从句)
a.Poeple all over the world recognizethat two loving parents are better than one.
a.People often saythat the saddest thing about youth is that it is wasted on the young.
a. People are increasingly optimisticabout the future of economic growth.