皮皮学，免费搜题
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【多选题】
关于防腐剂的正确叙述是:A.
甲醛能固定尿中有形成分
B.
甲苯可保持尿液化学成分不变
C.
浓盐酸能防止尿中激素被氧化
D.
甲苯于每30ml尿中加1ml
E.
甲苯在第一次尿中加数滴使薄膜
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皮皮学刷刷变学霸
举一反三
【单选题】A new technique_________, the yields as a whole increased by 20 percent.
A.
working out
B.
having worked out
C.
having been worked out
D.
to have been worked out
【单选题】________hard before, Tom is afraid of failing in the exam.
A.
Having been worked
B.
Not to have worked
C.
Having never worked
D.
Never have worked
【单选题】_______ , the girl worked in a hurry.
A.
Having swept the room
B.
Another room swept
C.
Having another room to sweep
D.
Having another room to be swept
【单选题】1 spent half an hour _________ this difficult math problem.
A.
having worked on
B.
to work on
C.
on work
D.
working on
【单选题】________ in the company for three years, Mark has become experienced in business negotiations. A) Having worked B) Have been working C) Have worked D) Worked
A.
Having worked
B.
Have been working
C.
Have worked
D.
Worked
【单选题】all day, I went to bed early.
A.
Working hard
B.
Worked hard
C.
Having worked hard
D.
To work hard
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