In Hillcrest School, 36% of middle school students are in Grade 6, 31% are in grade 7, and 33% are in grade 8. If a middle school student is selected randomly, what is the probability that the student is either in grade 6 or in grade 7? A) 0. 31 B) 0. 33 C) 0. 64 D) 0. 67
