—This morning your mobile phone was always busy. I couldn’t ________ to you until several attempts.—Oh, I’m sorry. I was discussing the price of our products with a client over the phone.

The survey shows that a large number of teenagers are ________ cigarettes nowadays.

. The ______ house is his.

While working in the countryside, the students         a great deal of knowledge on plant life.

People exposed to radiation are more _______ to suffer from certain forms of cancer, which can be ______ but can’t be ______at present.