宇宙中的大多数物质都被假定是“暗的”，即看不到的。研究已经表_爱下问搜题

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问题单项选择题

宇宙中的大多数物质都被假定是“暗的”，即看不到的。研究已经表明，如果很多星系群中的星系组成物质是可见的恒星，相对于其他星系的移动速度就会快得多。这一研究表明，星系在相当大的不可见的物质引力作用下运动。
下面哪个是上文依据的假设

A．运动星系速度的测量是极不可靠的。
B．重力的作用形式没有被特别好地理解。
C．对于上述星系中可见恒星的总的质量的估计是有一定把握的。
D．宇宙中不可见物质的大体组成部分已经被确定了。
E．上面提到的星系都毫无例外地向彼此移动。

答案

参考答案：C

解析：论证把“恒星相对于其他星系的移动速度快”的原因归于“暗的物质”，那么必须假设不存在其他原因，例如，是由于目前可见恒星的总质量估计不准造成的。C选项就是上述无他因假设。

完形填空

To celebrate the end of our exams, my friends and I went to a fast food restaurant. We    hamburgers and Coca Cola at the counter. When our    came, I started walking towards an empty table. By bad luck, my bag strap(带子) got    on a chair and the tray(托盘) that I was holding slipped(滑)    my hands and went flying in the air. The tray, and its contents,    on a man who was just about to    a bite of his sandwich. I stared, greatly    , as the drinks soaked(浸湿) his white shirt.
Then I    my eyes and prepared myself for his burst of   . Instead, he said "It’s OK" to     me before he disappeared into the washroom.
Still shaky and unsure    to do next, my friends and I went to a table and sat there, trying our best to look   . A moment later, the man came out of the washroom, and    our table. My heart almost stopped   . I thought he was going to ask for my father's    and call him.
To my surprise, he merely smiled at us, handed us some cash and said,"    yourself new hamburgers."
He then walked    without even finishing his food.
He could have made what was already an uncomfortable situation worse,    he chose a different way and gave us a reason to believe that there is still    in this world. I'll never     his actions.

A．discouraged

B．disappointed

单项选择题

碳素工具钢是含碳量为0.65％-1.35％的优质高碳钢，其热处理后的硬度可达（）。

A、60-64HRC

B、70HRC以上

C、50-55HRC

D、200HBS以上