immune a.免疫的；不受影响的；免除的
例句：About 93 percent of U.S. residents are immune to measles either because they were vaccinated or they had the disease as a child.
句意：大约93%的美国居民对麻疹是免疫的，他们要么因为接种过疫苗，要么就是小时候得过麻疹。

本题选B。