题目

Find ways to praise your children often, ____ you’ll find they will open their hearts to you. A. till       B. or      C. and     D. but   答案：C4．如图表示某生态系统，下列说法正确的是（　　）A．①积累的毒素最多B．②与③是竞争关系C．④是消费者D．该生态系统只有一条食物链