They have leading experts in this field，and that’s __________ they’ve made important progress．

Who did the teacher______ an article for the wall newspaper?[ ]

.—Did yourfather come back early last night—Yes. It was not yet eight o’clock ______he arrived home.

Granny seems ill. Are you sure it’s _______

is no easy way to remember prepositions, as it is one area of English____ the rules seem very irregular.