单项选择题
Hearing a knock ______ the door, he hid himself ______ the door.
单项选择题 The monkey ______ the tree was eating the bananas ______ the tree.
单项选择题 Some new changes happened ______ the school ______ my absence.
单项选择题 The plan for a new airport have been scrapped ______ an extension to the old one.
