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【单选题】
在粗糙水平面上放着一个三角形木块abc，在它的两个粗糙斜面上分别放有质量为m 1 和m 2 的两个小物体，m 1 >m 2 ，如图所示.若三角形木块和两物体都是静止的，则粗糙水平面对三角形木块（）A.
有摩擦力的作用，摩擦力的方向水平向右
B.
有摩擦力的作用，摩擦力的方向水平向左
C.
有摩擦力的作用，但摩擦力的方向不能确定，因为m1、m2、θ1､θ2的数值并未给出
D.
以上结论都不对
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举一反三
【单选题】It can be inferred from the text that______.
A.
once customers' misfortunes happen, they can get compensation from companies
B.
once customers' misfortunes happen, they can't get compensation from companies
C.
according to current law, the information on the products was provided for the benefits of customers
D.
according to current law, the information on the products was provided as protection against legal liability
【单选题】客户采购了一台路由器，如果此路由器性能指标为平均无故障工作时间MTBF>Y148年，平均维修时间MTTR
A.
99.9%
B.
99.99%
C.
99.999%
D.
99.9999%
【单选题】客户采购了一台路由器,如果此路由器性能指标为平均无故障工作时间MTBF>Y14 8年,平均维修时间MTTR
A.
99.9%
B.
99.99%
C.
99.999%
D.
99.9999%
【单选题】一 Do you happen to know Maria's address? ( )
A.
Not offhand , but I can look it up in my address book.
B.
Really? I thought you' d be excited about it.
C.
No , I don't , but that's a good question.
【简答题】密封件材料应具备哪些性能?哪些材料可以作为O形密封圈的制作材料?
【单选题】听力原文： I grew up in a small town. My father raised chickens and ran a construction company. I was barely 10 years old when my dad gave me the responsibility of feeding the chickens and cleaning up the ...
A.
Because he was a cook at a country-music club.
B.
Because he performed for guests while he worked as a cook.
C.
Because he often sang while cooking.
D.
Because he liked singing better than cooking.
【单选题】客户采购了一台路由器设备,如果此路由器性能指标为平均无故障工作时间MTBFW5000,平均维修时间MTTRSOQ 5则此路由器可靠性为:
A.
99.9%
B.
99.99%
C.
99.999%
D.
99.9999%
相关题目：
【单选题】客户采购了一台路由器,如果此路由器性能指标为平均无故障工作时间MTBF>Y14 8年,平均维修时间MTTR
A.
99.9%
B.
99.99%
C.
99.999%
D.
99.9999%