I'll get in touch with you ______ I come back from vacation.

• if

• when

Hurry up! ______ we don't hurry, we'll be late.

• if

• when

_____ they don't come soon, we'll eat without them.

• if

• when

You always have to raise your seat _____ before you land or take off on a plane.

• after

• until

• before

• as soon as

Nick is reading a novel _______ Jack is reading a cartoon.

• while

• if

• but

hệ sinh thái

• system

• ecosystem

• extinction

___________ we cook pies, we wash our hands.

• before

• after

• untill

• no

Students should learn some practical ways that help to __________ pollution.

• save

• cure

• reduce

• shorten

Parents should teach children not to __________ wastes on the road.

• litter

• poison

• cause

• pick up