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What are the functions of actin filaments?A.
Actin filaments, polymers of the protein actin, are present in most eukaryotic cells and are essential for many of the cell’s movements, especially those involving the cell surface. Without actin filaments, for example, an animal cell could not crawl along a surface, engulf a large particle by phagocytosis, or divide in two.
B.
Like microtubules, many actin filaments are unstable, but by associating with other proteins they can also form stable structures in cells, such as the contractile apparatus of muscle cells. Actin filaments interact with a large number of actin-binding proteins that enable the filaments to serve a variety of functions in cells.
C.
Depending on which of these proteins they associate with, actin filaments can form stiff and stable structures, such as the microvilli on the epithelial cells lining the intestine or the small contractile bundles that can contract and act like tiny muscles in most animal cells .
D.
They can also form temporary structures, such as the dynamic protrusions formed at the leading edge of a crawling cell or the contractile ring that pinches the cytoplasm in two when an animal cell divides. Actin-dependent movements usually require actin’s association with a motor protein called myosin.
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【单选题】My cousin _____________ and found himself on the floor, not on the bed. [ ]
A.
got up
B.
woke up
C.
grew up
【简答题】梅利莎发现很难与员工卡洛尔相处。卡洛尔是前台有经验的员工,在饭店工作已经3年了。梅利莎发现自从她几个月到任以来,卡洛尔一直对她不够友好,拒绝回答她提出的有关工作程序的问题。卡洛尔向梅利莎承认,自己一直想晋升到梅利莎现在的职位,对公司从外面聘人很不满意。梅利莎冥思苦想,希望卡洛尔能接受她这个主管。有几次,梅利莎发现卡洛尔在与其他前台员工说笑,可当她一走近,他们就走开了。梅利莎确信卡洛尔肯定是在挑拨她...
【单选题】下列关于表格的说法中不正确的是()。
A.
单击插入选项卡中的表格按钮，然后拖出所需要的行数和列数，则可快速
B.
在文档中插入空白表格。
C.
在单元格中输入的文本占满列宽时自动换行。
D.
组合键可以来操纵表格。
E.
只能在文档的开始处才能插入表格。
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