逆转录病毒载体系统的缺点是： A．感染细胞量大 B．稳定性较好_爱下问搜题

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问题单项选择题

逆转录病毒载体系统的缺点是：

A．感染细胞量大
B．稳定性较好
C．病毒滴度较高
D．只能整合至分裂相的细胞
E．转染谱广

答案

参考答案：D

解析：[解题思路] 逆转录病毒载体系统的特点。逆转录病毒载体系统的特点包括转染谱广、感染细胞量大、稳定性较好、病毒滴度较高，D选项与E选项矛盾，故E选项是正确答案。

单项选择题 B型题

胆囊造影前一日晚餐应进（）

A.高脂肪餐

B.无脂低蛋白高糖餐

C.口服造影剂

D.低蛋白低脂肪餐

E.禁食

完形填空

阅读下面短文，掌握其大意，从每题所给的A、B、C、D四个选项中，选出最佳选项。
James’s New Bicycle
James shook his money box again. Nothing! He carefully __36__ the coins that lay on the bed. $24.52 was all that he had. The bicycle he wanted was at least $90! __37__ on earth was he going to get the __38__ of the money?
He knew that his friends all had bicycles. It was __39__ to hang around with people when you were the only one without wheels. He thought about what he could do. There was no __40__ asking his parents, for he knew they had no money to __41__.
There was only one way to get money, and that was to __42__ it. He would have to find a job. __43__ who would hire him and what could he do? He decided to ask Mr. Clay for advice, who usually had __44__ on most things.
“Well, you can start right here,”said Mr. Clay. “My windows need cleaning and my car needs washing.”
That was the __45__ of James’s odd-job(零工) business. For three months he worked every day after finishing his homework. He was amazed by the __46__ of jobs that people found for him to do. He took dogs and babies for walks, cleared out cupboards, and mended books. He lost count of the __47__ of cars he washed and windows he cleaned, but the __48__ increased and he knew that he would soon have __49__ for the bicycle he longed for.
The day __50__ came when James counted his money and found $94.32. He __51__ no time and went down to the shop to pick up the bicycle he wanted. He rode __52__ home, looking forward to showing his new bicycle to his friends. It had been hard __53__ for the money, but James knew that he valued his bicycle far more __54__ he had bought it with his own money. He had __55__what he thought was impossible, and that was worth even more than the bicycle.

B．introduction

C．requirement

C．suitability