图中神经元a、b与痛觉传入有关，神经元c能释放脑啡肽，脑啡肽具有镇痛作用．请回答问题：

分母是8的所有真分数的和是2．

        One day, when Zhou Kai’s mother saw him ____ (head) towards the front door without a jacket on, she eyed him with____ (anxious). She asked him____ (put) on my jacket and he did ____ he was told.

         His mother always makes sure the family eat ____ . For example, they have fish four times a week. Zhou Kai very ____ (rare) gets colds but last week he had____  bad cold and a bit of a fever. How come? That’s____ he was stupid____  to play football in the rain. So you can see how crazy he is____  football.