皮皮学，免费搜题
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【单选题】
下列哪一种单糖没有手性碳原子?A.
葡萄糖
B.
甘油醛
C.
赤藓糖
D.
二羟基丙酮
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【多选题】What are some of the problems associated with fuel cell technology? Click on 2 answer choices.
A.
Noise pollution
B.
Public acceptance
C.
Supplies of hydrogen
D.
Investment in infrastructures
【单选题】What did Fabio Hendry and Seongil Choi do according to the news ?
A.
They created a method called selective laser sintering.
B.
They used metal or plastic powder for various objects.
C.
They developed a method for hardening the nylon powder into solid objects.
D.
They exhibited 12 artistic stools.
【单选题】His grandparents used to ________ a walk after dinner, but now they are used to ________ a walk after breakfast.
A.
take, take
B.
taking, taking
C.
taking, take
D.
take, taking
【单选题】He used to to school by bike but he is used to to school now.
A.
go; walking
B.
go; walk
C.
going; walk
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