Wash your hands---you have dinner.A.before B.but C.when D.so

Wash your hands＿＿＿you have dinner.A.before B.but C.when D.so 还有几题：Early men found fire very＿＿＿millions of years ago.A.use B.useful C.useless D.usesOnly a quarter of the Earth is＿＿＿.A.oceans B.land C.forests D.seas