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【多选题】
《宪法》规定,我国的基本国策包括( )A.
计划生育
B.
改革开放
C.
男女平等
D.
保护环境
E.
节约能源
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【多选题】下列对于塑料注射模标准模架派生型组合的描述正确的是( )。
A.
以直浇口为主
B.
以点浇口为主
C.
组合尺寸系列与基本型相同
D.
组合尺寸系列与基本型不同
E.
以多分型面为主
【单选题】Which pair of words best describes the feeling during the first stage of culture shock?
A.
Lonely and depressed.
B.
Bored and homesick.
C.
Happy and thrilled.
D.
Angry and frustrated.
【单选题】Which pair of words/phrases indicates contrast?
A.
Gigantic structure great desert expanse
B.
A call for prayer men and women with the shisha
C.
Chaos maddening
D.
Coffee shops pyramids
【单选题】Which pair of words is NOT a minimal pair?
A.
cat / bat
B.
put / but
C.
jig /pig
D.
sit / bit
【多选题】How does crossing-over occur between the duplicated maternal and paternal chromosomes in each bivalent?
A.
In sexually reproducing organisms, the pairing of the maternal and paternal chromosomes is accompanied by homologous recombination, a process in which two identical or very similar nucleotide sequences exchange genetic information. A similar process takes place when homologous chromosomes pair during the long prophase of meiosis I. In this case, the recombination occurs between the non-sister chromatids in each bivalent, rather than between the identical sister chromatids within each duplicated chromosome. In the process, the maternal and paternal homologs can physically swap homologous chromosomal segments, an event called crossing-over.
B.
Crossing-over is a complex, multistep process that is facilitated by the formation of a synaptonemal complex. As the duplicated homologs pair, this elaborate protein complex helps to hold the bivalent together and align the homologs so that strand exchange can readily occur between the non-sister chromatids. Each of the chromatids in a duplicated homolog (that is, each of these very long DNA double helices) can form a crossover with either (or both) of the chromatids from the other chromosome in the bivalent.
C.
By the time meiotic prophase ends, the synaptonemal complex has disassembled, allowing the homologs to separate along most of their length. But each bivalent remains held together by at least one chiasma (plural chiasmata), a structure named after the Greek letter chi, χ, which is shaped like a cross. Each chiasma corresponds to a crossover between two non-sister chromatids. Most bivalents contain more than one chiasma, indicating that multiple crossovers occur between homologous chromosomes. In human oocytes—the cells that give rise to the egg—an average of two to three crossover events occur within each bivalent.
D.
Crossovers that take place during meiosis are a major source of genetic variation in sexually reproducing species. By scrambling the genetic constitution of each of the chromosomes in the gamete, crossing-over helps to produce individuals with novel assortments of alleles. But crossingover also has a second important role in meiosis: it helps ensure that the maternal and paternal homologs will segregate from one another correctly at the first meiotic division.
【单选题】Which pair of words is alliterative?
A.
pain, Spain
B.
flower, float
C.
apple, April
D.
fast, last
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