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【简答题】
He said the local school district coached teachers on how to use software for online teaching. They asked teachers not to _________ they had planned for the school term.
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举一反三
【单选题】If two pair-elements of a kinematic pair have surface contact or its equivalent, the kinematic pair is known as a ( ).
A.
higher pair
B.
gear pair
C.
lower pair
D.
cam pair
【单选题】If two pair-elements of a kinematic pair have surface contact or its equivalent, the kinematic pair is known as a ( ).
A.
higher pair
B.
lower pair
C.
gear pair
D.
cam pair
【简答题】听长对话，选择正确答案。对话读两遍。 1. What does the woman want to buy? A. A pair of jeans B. A pair of running shoes C. A pair of trousers 2. How much is the black pair? A. 25 dollars B. 45 dollars C. 50 dollars 3. W...
【单选题】My brother has five _____ in his room. [ ]
A.
pair of shoe
B.
pairs of shoe
C.
pair of shoes
D.
pairs of shoes
【单选题】The writer mentions______as a pair to indicate that people should have moderate feelings of guilt.
A.
eccentric people and fashionable people
B.
overanxious people and less sociable people
C.
sociable people and healthy people
D.
reserved people and radical people
【单选题】欲配制pH=6.50的缓冲溶液,用下列何种酸最好
A.
(CH3)2AsO2H)(Ka=6.40×10-7)
B.
CICH2COOH (Ka=1.40X10-3)
C.
CH3COOH(Ka=1.76×10-5)
D.
HCOOH(Ka=1.77×10-4)
【单选题】欲配制 pH=6.50 的缓冲溶液,最好选用 _____
A.
(CH 3 ) 2 AsO 2 H ( K a Θ =6.40×10 -7 )
B.
ClCH 2 COOH ( K a Θ =1.40×10 -3
C.
CH 3 COOH ( K a Θ =1.76×10 -5
D.
HCOOH ( K a Θ =1.77×10 -4
【单选题】欲配制pH约为9的缓冲溶液,下列缓冲对选择哪一对最合适?()。
A.
NaH 2 PO 4 -Na 2 HPO 4 ； K a2 =6.23×10 -8
B.
HCN-NaCN ； K a =4.93×10 -10
C.
NH 3 -NH 4 Cl ； K b =1.76×10 -5
D.
HAc-NaAc ； K a =1.76×10 -5
【单选题】汽化器式燃油系统中 , 喷油嘴出口与浮子式内燃油液面高度的关系为
A.
喷油嘴出口等于浮子室内燃油液面高度
B.
喷油嘴出口低于浮子室内燃油液面高度
C.
喷油嘴出口高于浮子室内燃油液面高度
D.
两者的高度关系不定
【单选题】欲配制pH=6.50的缓冲溶液,下列酸最好的是:( )
A.
(CH 3 ) 2 AsO 2 H (K a =6.40×10 -7 )
B.
ClCH 2 COOH (K a =1.40×10 -3 )
C.
CH 3 COOH (K a =1.76×10 -5 )
D.
HCOOH (K a =1.77×10 -4 )
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