powerless根据嘉宾观点“We experiment on animals because they are powerless to stop us，”可知答案是powerless。

Presenter: Good evening and welcome to Issue for Today. Our topic tonight is experiment on animals and to start the discussion we have a strongly argued appeal from Jeff Sachs of the animal’s rights organization Animal Aid. Now Jeff, what’s all the fuss about? After all, 85 percent of doctors support experiments on animals.
Jeff: This is first and foremost a moral question. What kind of people are we? As humans, we live in a society which protects the rights of the weak. We take care of the sick, the old and the disabled and punish those who are violent to others. But we also have a darker, cruel side. I believe that we experiment on animals because they are powerless to stop us, and we count their pain as unimportant when measured against our own interests. We live unhealthy lives and make animals suffer in the search for cures for our illnesses. We even see the production of a new lipstick as a good enough reason to inflict pain on animals. It’s not that we think animals can’t feel pain--we know very well that they do. And it’s dangerous to say that we use animals in experiments because they lack our intelligence. After all, this argument would allow us to experiment on mentally handicapped humans. Animals have feelings. Like us, they can suffer pain, fear and mental agony. Like us, each has a life to live. A rat’s life is important to a rat, whatever value a human may place on it. Why should one individual animal be made to suffer for the supposed benefits of people? Is it right to kill one human being in an experiment to save thousands of others? What if that human being were you?
Presenter: Yeah, well, thank you. Now, let’s hear what you, the audience, and you at home think...