He never rides first class except on the short hauls.他除了短途旅行之外从不坐头等车.We went on long bicycle rides together...我们一起骑自行车长途旅行。Heigh, heigh! The devil rides upon a fiddlestick. What's the matter?嗨嗨! 真是新鲜事儿. 究竟怎么回事?She r...
另两个为胸腺嘧啶和胞嘧啶, 即称为嘧啶的单环结构.The other two, thymine and cytosine, are single ring structures called pyrimidines.直到不久以前,人们对胸腺的功能尚不明了.The function of the thymus was unknown until relatively recently.动物的免疫系统由两个主要部分组成,即胸腺和骨髓系统.I...