答案：C

考察名词性从句。What引导主语从句what made our school proud in 2011，并在句中作主语。That引导表语从句，that more than 40% of the  students had been admitted to key universities.这个表语从句很完整，that只起引导作用，不充当任何成分。结合句意可知C正确。句意：2011年让我们学校自豪的是超过百分之40的学生被重点大学录取。