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【单选题】
配气机构的作用是按照发动机每一气缸内所进行的工作循环和发火次序的要求，定时开启和关闭各气缸的进、排 气门，使（）得以及时进入气缸，废气得以及时从气缸排出。A.
新鲜空气
B.
燃油
C.
新鲜可燃混合气
D.
机油
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【多选题】What are the functions of reverse transcriptases?
A.
Reverse transcriptases catalyze three different reactions: (1) RNAdependent DNA synthesis, (2) RNA degradation, and (3) DNA-dependent DNA synthesis. Like many DNA and RNA polymerases, reverse transcriptases contain Zn 2+ .
B.
Each transcriptase is most active with the RNA of its own virus, but each can be used experimentally to make DNA complementary to a variety of RNAs. The DNA and RNA synthesis and RNA degradation activities use separate active sites on the protein. For DNA synthesis to begin, the reverse transcriptase requires a primer, a cellular tRNA obtained during an earlier infection and carried in the viral particle.
C.
This tRNA is base-paired at its 3′ end with a complementary sequence in the viral RN The new DNA strand is synthesized in the 5′ → 3′ direction, as in all RNA and DNA polymerase reactions. Reverse transcriptases, like RNA polymerases, do not have 3′ → 5′ proofreading exonucleases.
D.
They generally have error rates of about 1 per 20,000 nucleotides added. An error rate this high is extremely unusual in DNA replication and seems to be a characteristic of most enzymes that replicate the genomes of RNA viruses. A consequence is a higher mutation rate and faster rate of viral evolution, which is a factor in the frequent appearance of new strains of disease-causing retroviruses.
【单选题】根据《建设工程工程量清单计价规范》(GB 50500—2008)的规定，下列选项中，不属于按设计图示尺寸以面积计算墙面镶贴块料的是( )。
A.
石材墙面
B.
碎拼石材墙面
C.
装饰板墙面
D.
块料墙面
【多选题】下列选项中，属于塑料板面层一般项目的是（）
A.
塑料板面层所用的塑料板块卷材的品种、规格、颜色、等级应符合设计要求和现行国家标准的规定
B.
板块的焊接，焊缝应平整、光洁，无焦化变色、斑点、焊瘤和起鳞等缺陷，其凹凸允许偏差为±0.6mm。焊缝的抗拉强度不得小于塑料板强度的75%
C.
塑料板面层应表面洁净，图案清晰，色泽一致，接缝严密、美观。拼缝处的图案、花纹吻合，无胶痕；与墙边交接严密，阴阳角收边方正
D.
镶边用料应尺寸准确、边角整齐、拼缝严密、接缝顺直
E.
面层与下一层的粘接应牢固，不翘边、不脱胶、无溢胶
【单选题】关于太极二章第一步，下列叙述正确的是：
A.
向左侧转身成左前侧丁字步，左手下格挡。
B.
向右侧转身成右前侧丁字步，左手下格挡。
C.
向左侧转身成左前侧丁字步，右手下格挡。
D.
向左侧转身成左前侧弓步，左手下格挡。
【单选题】What is the difference between a reverse auction and mass customization?
A.
Reverse auction is most often found in B2B whereas mass customization is often found in B2C.
B.
Reverse auction requires a bid from consumers whereas mass customization requires a bid from suppliers.
C.
Mass customization require a click-and-mortar environment; reverse auctions do not.
D.
Mass customization can sell digital products; reverse auctions sell commoditylike products.
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