1. Not all the skin diseases are contagious. 不是所有的皮肤病都是会传染的。
2. Happiness is contagious—— find someone who is happy and stand close to them. 快乐是可以传染的——所以找些快乐的人，然后向他们靠拢。
3. The researchers found that happiness really is contagious. Sadness also spread among friends, but not as much as happiness. 研究员发现，快乐真的会传染。虽然悲伤同样能在朋友间蔓延，但还是不及快乐。
英英解释
adj.
1. easily diffused or spread as from one person to another
2. (of disease) capable of being transmitted by infection
