I was deeply impressed by the hostess' ______ and enjoyed the dinner party very much.
A. hostility
B. indignation
C. hospitality
D. humanity
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John did not distinguish himself as a student, but he was very active in class.（）
A. 约翰隐藏了自己是——名学生的身份，这具有一定的积极意义。
B. 作为学生，约翰不能与其他学生区别开来，这样恰恰使他能在班上起作用。
C. 在班上，约翰的表现显得他并不像是学生，但他很活跃。
D. 约翰当年并不是出色的学生，但他在班上很活跃。
The entire family is ______ in scientific research.
A. dipped
B. immersed
C. saturated
D. submerged
下列DNA模型中，属于左手螺旋的是（）
A. Z-DNA
B. C-DNA
C. B-DNA
D. A-DNA
The basic causes are unknown, although certain conditions that may lead to cancer have been ______.
A. identified
B. guaranteed
C. notified
D. conveyed
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