HELP KEEP THIS AREA CLEAN.

HELP KEEP THIS AREA CLEAN. help keep the environment clean意思 Friends of the Earth help keep the environment clean.“ keep This house is easy to keep clean. help,air,trees,the,keep,clean连词成句句号 We must help ______(keep) our enviroment clean. trees help keep the air clean help后可以直接跟keep吗 You may borrow this book______you keep it clean. Friends of the Earth help keep the environment clean.对“ keep street cleaners help keep our city__.a,clean b,cleaning c,to It's a p____ way to help keep our city clean and tidy. planting tree can help( )the air clean 是用keep 的什么时态?