所谓退出壁垒是指企业在退出某一行业市场时所遇到的阻碍。下列因素中属于退出壁垒的是（）

下列关于蛋白质合成的叙述正确的是（）

A.一种密码子可以编码多种氨基酸

B.反密码子与密码子互补呈严格的碱基配对关系

C.体内所有的氨基酸都有相应的密码子

D.肽链合成是从N端向C端进行的

E.氨基酸的氨基被活化

Mr. Faugel was convinced that student nervousness had affected their scores; to reduce the anxiety of these students who had already been tested, he gave 22 of them a beta blocker before readministration of the test. Their scores improved significantly. The other 8 students (who did not receive the beta blockers) improved only slightly. Second-time test-takers nationwide had average improvements which were similar to those in Faugel’’s non-beta blocker group. Beta blockers are prescription drugs which have been around for 25 years. These medications, which interfere with the effects of adrenalin, have been used for heart conditions and for minor stress such as stage fright. Now they are used for test anxiety. These drugs seem to help test-takers who have low scores because of test fright, but not those who do not know the material. Since there can be side effects from these beta blockers, physicians are not ready to prescribe them routinely for all test-takers.

Beta blockers work on some physical and emotional symptoms because they________.

A．fool a person into a healthier stance

B．interfere with the effects of adrenalin

C．produce side effects worse than the symptoms

D．primarily change human thought processes

甲公司为一投资项目拟定了甲、乙两个方案，
请您帮助作出合理的投资决策，相关资料如下：
(1)甲方案原始投资额在建设期起点一次性投入，项目计算期为6年，净现值为19.8万元；
(2)乙方案原始投资额为100万元，在建设期起点一次性投入，项目计算期为4年，建设期为1年，运营期每年的净现金流量均为50万元。
(3)该项目的折现率为10%。
要求：
(1)计算乙方案的净现值；
(2)用年等额净回收额法作出投资决策；
(3)用方案重复法作出投资决策；
(4)用最短计算期法作出投资决策。

让不同年龄阶段、个性、特长的护理人员充分发挥个人潜能，体现了护理人员编设原则中的哪一原则？（）

A.优化组合原则

B.满足病人需要原则

C.合理结构原则

D.以人为本原则

E.经济效能原则