A
句意:养成坏习惯很容易,但要改掉却很难。
easy 容易的 hard 难的
根据第一段后半句:so it's easier to fall into bad habits than into good ones. (因此,养成坏习惯比养成好习惯更容易。)
以及第二段第5-7行:
When they get bigger, the habits become stronger and stronger, so that they can no longer get rid of them. (当他们变大的时候,习惯变得越来越强,以至于他们再也无法摆脱它们。)
可知坏习惯养成很容易,然而,想改掉却很难。
故选A