【单选题】Activin is a protein that normally exists in a gradient within certain tissues in developing embryos. Certain undifferentiated cells cultured without activin produce epidermal cells. However, activin ...
【简答题】听下面一段材料,回答1-3题。 1. Why didn't Jim write to the woman last month? [ ] A. Because he couldn't write. B. Because he was traveling in another country. C. Because he never wrote letters when he was on ...
【简答题】Join the two independent clauses to make a compound sentence. Use one of the coordinating conjunctions (and, but, for, or, nor, so, yet). Remember to use a comma before the connecting word. a. He enjo...
【简答题】完形填空。 Last January I was given a chance to work in another country. At first, I lived a 1 life, but soon I met a group of new friends and they were really nice. Then something 2 happened. One of our f...