皮皮学，免费搜题
登录
搜题
【多选题】
令 P1 是 的划分,P1 的成员是 , , Q 是有理数集合 (符号 就是 ). 令 /P1 是 相对于 P1 的粘合空间, /P1 是投影. (重温: /P1 的元素是 P1 的成员, 是 P1 中含 x 的成员, /P1 上的拓扑是 /P1 上令 连续的最大拓扑) 命题: /P1 是平庸空间(即粘合拓扑是平庸拓扑 { /P1 }) 题目:以下是以上命题的证明尝试,那句话是真的?A.
设 /P1 是 /P1 的非空开集. 要证它是 /P1 .
B.
因为 U 开，所以 是 中的开集；因为 U 非空，所以存在区间 .
C.
所以对所有 , .
D.
所以 , 从而 /P1.
E.
ABCD 都不真
手机使用
分享
复制链接
新浪微博
分享QQ
微信扫一扫
反馈参考答案：
举一反三
【单选题】关于期门穴位的定位正确的是( )
A.
在侧腹部,当第11肋游离端的下方
B.
在胸部,乳头直下,第6肋间隙,前正中线旁开4寸
C.
在侧腰部,章门后1.8寸,当第12肋骨游离端的下方
D.
在上腹部,当乳头直下,第7肋间隙,前正中线旁开4寸
E.
在侧腹部,章门下1.8寸,当第11肋骨游离端下方垂线与脐水平线的交点上
【单选题】中极穴的定位正确的是( )。
A.
在下腹部，前正中线上，当脐中下3寸
B.
在下腹部，前正中线上，当脐中下4寸
C.
在下腹部，前正中线上，当脐中下5寸
D.
在上腹部，前正中线上，当脐中上3寸
E.
在上腹部，前正中线上，当脐中上4寸
【简答题】Manage relationships with people around you The hierarchy in student life is relatively straight-forward. In c______, very different dynamics are involved in the workplace as you i_____ with many grou...
【多选题】How are tRNAs processed in bacteria and eukaryotes?
A.
Most cells have 40 to 50 distinct tRNAs, and eukaryotic cells have multiple copies of many of the tRNA genes. Transfer RNAs are derived from longer RNA precursors by enzymatic removal of nucleotides from the 5′ and 3′ ends. In eukaryotes, introns are present in a few tRNA transcripts and must be excised. Where two or more different tRNAs are contained in a single primary transcript, they are separated by enzymatic cleavage.
B.
The endonuclease RNase P, found in all organisms, removes RNA at the 5′ end of tRNAs. This enzyme contains both protein and RN The RNA component is essential for activity, and in bacterial cells it can carry out its processing function with precision even without the protein component. RNase P is another example of a catalytic RNA, as described in more detail below. The 3′ end of tRNAs is processed by one or more nucleases, including the exonuclease RNase D.
C.
Transfer RNA precursors may undergo further posttranscriptional processing. The 3′-terminal trinucleotide CCA(3′) to which an amino acid is attached during protein synthesis is absent from some bacterial and all eukaryotic tRNA precursors and is added during processing. This addition is carried out by tRNA nucleotidyltransferase, an unusual enzyme that binds the three ribonucleoside triphosphate precursors in separate active sites and catalyzes formation of the phosphodiester bonds to produce the CCA(3′) sequence. The creation of this defined sequence of nucleotides is therefore not dependent on a DNA or RNA template—the template is the binding site of the enzyme.
D.
The final type of tRNA processing is the modification of some bases by methylation, deamination, or reduction. In the case of pseudouridine, the base (uracil) is removed and reattached to the sugar through C-5. Some of these modified bases occur at characteristic positions in all tRNAs.
相关题目：
参考解析：
知识点：
题目纠错 0
发布
