一、单选题 1.—What should we do to keep the air clean? ( ) —__________. A.We should ride bike more often B.We can go for a walk C.We need to walk 2.Lu Ban was ___________ work on a mountain. ( ) A.at B.on C.in 3.Ben and his family spent their holiday in London. They visited ______ today. ( ) A.the Great Wall B.the Palace Museum C.the British Museum 4.My father and I _______ like playing chess. ( ) A.all B.both C.with