用SO3磺化要注意防止（）等副反应。
A.多磺化，
B.氧化，
C.焦化
参考答案：A, B, C
35.It is said that dogs will keep you _____ as long as you want when you are
feeling lonely.
A．accompany
B．company
C．friend
D．safely
铸铁给水管道埋地敷设的直线方向弯曲允许每（）m偏差为15mm。
A．8
B．10
C．12
D．14
