Only those ____knew well could be let in.
It is _____ my father worked _____ I work now.
It is the protection for the trees _______ really matters, rather than how many trees are planted.
It is _______ he often fails in exams ______ makes his parents worried about him.
Who are making so much noise in the garden? —_______ the children.
It was lack of money, not of effort, _____ defeated their plan.