A: Can I help you?
B: Yes. The green scarf is very pretty. How much is it?
A: It's $100.
B: It's too expensive. What about the sunglasses?
A: They're $20.
B: They're cheap. I like them.
蛇为变温动物,也就是体温随着外界的温度而改变,故推测其较不适合生活于何种生活环境( )
已知抛物线y=﹣mx2+4x+2m与x轴交于点A(α,0),B(β,0),且1α+1β=﹣2
“脚踏黄河水倒流,搬来泰山做枕头;决心苦战十五年,赶上英国不发愁”。这首新民歌创作的时代背景是