It was just a ________remark - I wasn’t really serious.

Air is________and of no smell but we can feel its motion when there is a wind. 

My neighbor is as ___as a young man and dislikes sitting around doing nothing all day．

There is a wide ________of reference books to be found, so ________you look for some material needed, you can turn to me.

Jack is late again. It is       of him to keep others waiting.