2 . How to protect children from unsuitable material on some websites while encouraging them to use the Internet __________ in many areas of the world.

A．have long been discussed	B．has long been discussed
C．were long been discussed	D．was long been discussed

3 . The Russian scientists                       the vaccine against Covid-19.

A．are said to be developed	B．are said to have developed
C．had said to develop	D．have said to have been developed

4 . The letter_____ （write） by Lin Tao now．(所给词的适当形式填空）

5 . Many a house______in the powerful earthquake so far, so the homeless survivors have to stay in tents for the time being.

A．was damaged

B．were damaged

C．has been damaged

D．have been damaged

6 . The belief _______ people find it more convenient to shop online _______ in the research.

A．that; was proved	B．if; proved
C．which; was proved	D．whether; proved

7 . The silence in the dark building was scaring. No sound and voice____ heard at that moment.

A．were

B．was

C．is

D．are

8 . There is a new problem involved in the popularity of private cars________road conditions need________.

A．that；to be improved	B．which；to be improved
C．where；improving	D．when；improving