It is easier to go down a hill than to climb up a hill, so it is to fall into bad habit than into good ones. Bad habits do not come suddenly. They come little by little while people do not notice their danger. Some schoolboys first pick up bad habits in school and on the streets. When they cannot finish their lessons, they copy from their classmates. If they see bigger boys smoking, they also want to learn to smoke. When they are older, the habits become so strong that they can never get rid of them. From copying, they fall behind, then learn to steal, and smoking is bad for their health. At last they become worse and worse. How necessary it is that we get rid of the bad habits at the very beginning. Bad habits come   _  .
quickly suddenly quietly and slowly easily