移植到人体内的器官不易成活，从现代免疫学来看，移植的器官相当于（ ）
A．抗原
B．抗体
C．病原体
D．传染源
抗原是指引起人体产生抗体的物质．抗原的基本能力是免疫原性和反应原性．免疫原性又称为抗原性，是指能够刺激机体形成特异抗体或致敏淋巴细胞的能力．反应原性是指能与由它刺激所产生的抗体或致敏淋巴细胞发生特异性反应．
病原体指可造成人或动物感染疾病的微生物．
传染源是指能够散播病原体的人或动物．所以，移植到人体内的器官相当于抗原．
故选：A
As we know, being stressed is not a good thing. Here are some trips I would like to share with you. 1____________ Whenever you need help, turn to your parents and friends for help. It’s better to speak the worries out and get some advice from others, then you’ll feel more relaxed. 2____________ If you find yourself stressed out, find a way to let the feelings out. Do breathing exercises, listening to music, doing some sports and taking a walk may help. 3____________ When you calm down, it’s time to deal with your problem. You should find out what the problem is and figure out a way to solve it. If you can’t solve all of it at once, you may solve part of it. When you have found out what the problem is and started solving it, you will find your stress gone. 4____________ Every coin has two sides. Looking at the dark side can make you stressed and it won’t help solve your problem. So why not look at the bright side. 5____________ After you have solved the problem or part of the problem, buy yourself a gift, go to your favorite movie or just hang out with your friends. You will enjoy the feeling of being relaxed.
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