催化剂活性提高，氢转移活性增加，产品烯烃含量相对减少，使汽油辛烷值增加。（）
参考答案：错
His mother always tells him that he should be more careful, but ____ doesn't work.[ ]
A. which
B. she
C. he
D. it
高压及超高压管道及附近的连接方式一般是（）
A.法兰连接
B.焊接连接
C.螺纹连接
