The _______ class is at nine o'clock.
A：one
B：a
C：first
D：an
— Can you catch the ball?
— ________
下列昆虫的发育方式属于完全变态发育的是（ ）
①蝗虫②蝉③蜜蜂④蝇⑤蟋蟀⑥家蚕．
