They stood _____ at each other as if they were enemies.

never raises a finger to help me with thedinner, I the thanksgivingmeal from this afternoon till now.

In the past few years, research has suggested that Vitamin D may increase the level of serotonin（血清素）, one of the key nurotransmitters influencing our mood, and ________it helps to relieve mood disorders.

You can save money _______ you buy cheaper things.

Seeing the enemy, Gary was behaving as though nothing ______.[ ]