有问题就有答案
Q1：a class of+复数还是单数,请说明一下.
单数，一类。例如：考虑一类具有跳跃层的反应扩散系统。摘要讨论了一类具有跳跃层的反应扩散系统。
Q2：a class of 后可以接不可数名词吗
可以的。a class of: 表示种类的时候可以接可数也可以接不可数。It is a class of commerce , include grain oily purchase and sale , storage , carrying trade and grain oil to process trade. 它是商业的一个门类，包括粮油购销、仓储、运输业和粮油加工业。a crowd of: 呃啊我觉得这个应该…都是接可数、具象的名词。a crop of: 通常用于农作物吧！所以可以接不可数。That"s what I call a really good crop of cotton. 这棉花长得真叫一个棒。a flood of:（1）用作表示“泛滥的情况”后面都可以接。At present , there is such a flood of illicit publication that this article tries to deals with the viewpoint on the harmfulness and countermeasures in order to purify the library and develop the ecation function. 目前，在社会上非法出版物泛滥的情况下，为保护高校图书馆这块净土，充分发挥其教育作用。（2）用作表示量词的时候也是都可以。a flood of tears 泪流不止a flood of water 水很多，决堤的水PS 有一个很酷的用法！a flood of refugees 形容难民像洪水一样涌来！题主！推荐你用iciba！
Q3：a class of+复数还是单数，请说明一下。
单数，一类。。。。例如：A class of reaction diffusion system with jump layer is considered.摘要讨论了一类具有跳跃层的反应扩散系统。
Q4：a class of studentes对吗
表示隶属关系。一般来说，前面和后面的东西是同类的。Calss代表阶级，阶级是一个东西，学生是人。肯定是错的。
Q5：a class of classmates
D
Q6：翻译aclassofmilk这篇文章
One class of milkOne day, a poor boy who was selling goods from door to door to pay his way through school, found he had only one thin dime left, and he was hungry.He decided he would ask for a meal at the next house. However, he lost his nerve when a lovely young woman opened the door. Instead of a meal he asked for a drink of water! She thought he looked hungry so brought him a large glass of milk. He drank it so slowly, and then asked, How much do I owe you?" You don"t owe me anything," she replied. "Mother has taught us never to accept pay for a kindness." He said ... "Then I thank you from my heart." As Howard Kelly left that house, he not only felt stronger physically, but his faith in God and man was strong also. He had been ready to give up and quit. Many year"s later that same young woman became critically ill. The local doctors were baffled. They finally sent her to the big city, where they called in specialists to study her rare disease.Dr. Howard Kelly was called in for the consultation. When he heard the name of the town she came from, a strange light filled his eyes. Immediately he rose and went down the hall of the hospital to her room.Dressed in his doctor"s gown he went in to see her. He recognized her at once. He went back to the consultation room determined to do his best to save her life. From that day he gave special attention to her case.After a long struggle, the battle was won. Dr. Kelly requested the business office to pass the final bill to him for approval. He looked at it, then wrote something on the edge and the bill was sent to her room. She feared to open it, for she was sure it would take the rest of her life to pay for it all. Finally she looked, and something caught her attention on the side of the bill. She read these words ..."Paid in full with one glass of milk" (Signed) Dr. Howard Kelly.Tears of joy flooded her eyes as her happy heart prayed: "Thank You, God, that Your love has spread broad through human hearts and hands."There"s a saying which goes something like this: Bread cast on the waters comes back to you. The good deed you do today may benefit you or someone you love at the least expected time. If you never see the deed again at least you will have made the world a better place - And, after all, isn"t that what life is all about?