感觉答案A 比E 更像正确答案，为什么反而是E？

Lark Manufacturing Company initiated a voluntary Quality  Circles program for machine operators. Independent surveys of employee attitudes indicated that the machine operators participating in the program were less satisfied with their work situations after two years of the program's existence than they were at the program's start. Obviously, any workers who participate in a Quality Circles program will, as a result, become less satistied with their jobs.

Each of the following , if true, would weaken the conclusion drawn above except:

a.The second survey occurred during a period of recession when rumors of cutbacks an layoffs at Lark Manufacturing were plentiful.

e.The machine operators who participated in Quality Circles reported that, when the program started , they felt that particiaption might improve their work situations.

文中根本没提到the second survey啊，这不是不能weaken conclusion吗？正确答案为什么不是A呢？