As students, we must ________ on our studies and work hard instead of fooling around.

As students, we must ________ on our studies and work hard instead of fooling around.
A investigate B. memories C. approach D. concentrate
【答案】D
【解析】
【详解】考查动词词义辨析。句意：作为学生，我们必须集中精力于学习和努力学习，而不是游手好闲。A.investigate调查； B.memories记忆； C.approach接近； D.concentrate集中。根据instead of fooling around可知此处表示集中精力于学习和努力学习，固定短语concentrate on集中精力于，全神贯注于，专注于。故选D项。