---- Why is the cake so expensive?---- Maybe you don’t know a cake made of wheat costs less than _____ made of rice. 

Generally speaking, that city is ___ crowded than ___ in the same area.

— Why can’t the boy understand what the American teacher said?— Because he is a beginner, _______ he knows ________English.

Is ____ dangerous to swim in the river alone?

 Frankly speaking, ________ of them knew what the other was doing that morning.