— Helen, would you like to go to the park with me?
— .
A：Sorry, I wouldn't
B：Yes, I'd love
C：That's right
D：That's a good idea
关于地震、滑坡这两种地质灾害成因的说法，正确的是（ ）
在生态系统中，生物的种类、各种生物的____和____总是维持在相对稳定的状态，这种现象就叫做生态平衡．
