Gaining the knowledge ________ environmental protection will help you to become a qualified environmentalist.

With all the exercises needed ______, he went straight home, __________.

The      house smells as if it hasn’t been lived in for years. 

Computers and mobile phones, though they are indeed making our life ____ and more ____, have reduced the need for face-to-face communications.

Finding the ______look on the student’ s face, the professor felt _____about his explanation.