The b___ problem of the world is the interesting population

The b___ problem of the world is the interesting population This is the b___ of the game It's difficult to e____ the problem to the beginners.The visitors have to b___ down to get throughThe visitors have to b___ down to get through the stone door of the cave. The population of China is 1.3 b___ ABC is the b___ of learning English B___ is the opposite of top the problem of 翻译 Maria sings a song at the b___ of the class. There is man standing at the b___ of you. There are two b___ of tea on the table ABC is the b___ of learning English朋友们啊 B___ of the two girls wore a white dress today THE PROBLEM OF CHINA怎么样 statement of the problem是什么意思 statement of the problem是什么意思 confrontation of the problem是什么意思 a b___ of sugar The music sounds b___.