题目

--- Would you like to go on a trip with us? --- I’d love to, _______ I have too much work to do this weekend. A. because       B. and                   C. but             D. or 答案：C6．假定在一个由草原、鹿和狼组成相对稳定的生态系统中，把狼杀绝，鹿群的数量会（　　）A．迅速上升B．缓慢上升C．保持相对稳定D．先上升后下降又趋于稳定