To judge a child's standard, his marks in a test must be compared with marks gained by ______.

A．They only need a little food to survive
B．they are not afraid of the heat
C．They are too small to be attacked by other animals
D．they have a skin which is against water

A．it is cooler and safer for most animals at night
B．animals can find food in the dark
C．it is easy for animals to find water at night
D．animals cannot sleep at night