The students each _______________their own e-mail address.
It was ten o’clock _____ he came back home.
Was _____ that I saw last night at the concert?
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.