Experts have been warning _________ of the health risks caused by passive smoking.[ ]

Children are always asking all kinds of questions because they are ______ about the world they live in.

9 “Do you have any questions ________ clear to you?” the teacher asked

I ______ a good way of improving my English.

Are you two old acquaintances? —Yes, we _____ in the same neighborhood for quite a long time, though he went abroad with his family at 14