Professor Brown is becoming increasingly ________; last week he locked himself out of his laboratory three times.
句意：布朗教授越来越健忘了。上周他把自己所在实验室外面三次。oblivious意为“一个人不知道 周围发生什么事”。mindless愚笨的，不小心的。forgetful健忘的。absent缺席的。因此答案选C。