--Isn't it getting dark early tonight? ---I thinkl so. I can see that ____ is on already.

Unless you change your ________ towards your studies, you won’t make any progress, I believe. 

Parts of the cave have been badly affected by rain and           to the air.

Health problems are closely connected with bad eating habits and a ____ of exercise. 

 We are short of clean safe drinking water, which is found to be the ______ in many third world countries.