A：giving off
B：setting off
C：putting off
D：going off
粮食是人类生存和发展最基本的物质条件。
I am Bill Jones. I am a teacher of English. My wife is Linda Jones. She is a nurse. We have a daughter and a son. We have many friends.Look! These are my friends. This is Mr. Black. He is a worker. He works in a shoe factory He makes shoes there. That’s Mrs. Black. She is a worker on a farm near here. The girl is their daughter. She is a student. She is thirteen. The boy is their son. He is a young soldier（战士）. His name is Carl Black.
人们在清晨刚进入种植蔬菜的密闭大棚内，会感到气闷，主要原因是（ ）
