请英语高手解答几道英语选择题很急啊!

请英语高手解答几道英语选择题很急啊!
1、Half of the boys（ ）from the countryside.
A、come B、 comes C、is D was
2、Three kilometers（ ） a long way.You'd better take a taxi.
A、 are B、is C、was D、were
3、What I have told you（ ） a secret.Please don't tell others.
A、are B、is C、keep D、keeps
4、Most of the country（ ）grassland.
A、there are B、there is C、are D、is