主汽门法兰螺栓硬度多少为宜（）。
A.HB200---240
B.HB240---270
C.HB270---300
参考答案：B
用所给单词的适当形式填空。
1.1 want two________(tomato).
2. What________(do)you like to eat?
3. Linda likes to eat________(vegetable).
4. Jenny doesn't eat________(good) for lunch.
5. She________(not like) ice cream or salad.
安全困境
