根处于失水状态时，外界溶液浓度（W）与根细胞细胞液浓度（X）的关系是（　　）

—Is this your juice? —Yes, it____(are, is).

     Joan is an American girl. She lives in China now. She is in my class. Her parents work in China, too, but her brother works in the U.S.A. He often writes letters to them. Joan likes Chinese class very much, and likes speaking Chinese with us after class. Her father teaches us English well. We all like his class. On Sundays, Joan goes to the People's Park with her father and mother. Sometimes she goes shopping with her mother. They like the Chinese food very much. It's a happy family.

下列关于偏振光的说法中正确的是                                                        （   ）

在金鱼缸中放一些新鲜绿色水草，主要目的是（   ）