根据所学课文内容填空(每空0.5分，共计7分)

I am ___1__ of my sister but she has one serious ____2___. She can be really __3__. Although she didn’t know the best way of getting to places, she insisted that she __4___ the trip properly. Now I know that the proper way is always her way. I kept asking her, “When are we leaving and when are we ___5___ back?” I asked her whether she had looked at a map yet. Of course she hadn’t; my sister doesn’t care ___6__ details. So I told her that the   7  _ of the Mekong is in Qinghai Province. She gave me a ___8__ look-- the kind that said she would not change her mind. When I told her that our journey would begin    9  an altitude of more than 5,000 metres, she seemed to be excited about it. When I told her the air would be hard to ___10__ and it would be very cold, she said it would be an interesting ___11__. I know my sister well. ___12___ she has made up her __13__, nothing can change it. Finally, I had to give    14  .

用大肠杆菌作宿主表达重组DNA药物，缺点是（）。

A.蛋白质表达量低

B.生长慢

C.产物无糖基修饰

D.难以获得工程菌