人类MHC分子首先在人外周血______表面发现，故称HLA。

任务型阅读（共10空；每空1分，计10分） (每空一词)
Living in a city has both advantages and disadvantages. It is often easier to find work. If you go out, you can choose different vehicles. Besides, there are a lot of places of interest ot see. You can eat in good restaurants, visit museums, go to parks and watch films when you want to relax. However, living in a city is often very expensive. You must find a well-paid job, otherwise you will not have enough money to spend on the things you need. What’s more, the city is always crowded, noisy and dirty. It has become harder to find a good place where people can enjoy peace and fresh air as in the countryside.

1	Disadvantages
2 work in a city is often easier than in the 2. There’re lots of different vehicles for you to 3 There’re many 4 places to see. If you want to 5 ,you can eat in good restaurants, visit museums, go to parks and6.	You must have a well-paid job because living in the city will 7 you too much, otherwise you can’t8for the things you need. The city is not only full of  9 but also crowded and dirty. it has become more  10 to find a good place where people can enjoy peace and fresh air as in the countryside.