Trees help to k___ the air clean.其中k___能添什么单词?

Trees help to k___ the air clean.其中k___能添什么单词? Trees can help _____ the air in the city.A to clean B clean Your k___ to the question is wrong help,air,trees,the,keep,clean连词成句句号 We need three k___ to cut the birthday cake. trees help keep the air clean help后可以直接跟keep吗 1.paul is very k___.He likes to help other people. in order to k___ in good health Mrs Black is very k___ to me a half k___ of apple 填什么 Are you going to the k___?We need some salt and a bottle of We should plant more trees to make the air _____(clean). Jan