题目

    Easy Ways to Build Vocabulary It's not all that hard to build an advanced and large vocabulary. Like many things in life, it's 100．ongoing process, and the best part of the process is that there's enough room for improvement, 101．means you'll just keep getting better and better. Of course you have to work at it. You wouldn't think that a few 102．(month) of exercise in your teens would be enough 103． the rest of your life, and that's also true for building your vocabulary--you have to keep at it daily, and pretty soon you will find that you have an excellent vocabulary. On下列有关变异的叙述，正确的是A. 变异都是可遗传的 B. 变异对生物的生存都是有利的C. 生物的变异是普遍存在的 D. 变异都是由于遗传物质的改变引起的