Crystals are classified into how many different crystal systems?
a. 4
b. 5
c. 6
d. 7

There are 7 crystal systems: tetragonal, trigonal, hexagonal, cubic triclinic,  orthorhombic, and monoclinic. This is determined by point groups and lattices. 

Read the sentences below in 1962, i tried to enroll as the first black student at the university of mississippi. the governor of mississippi blocked my entrance which best describes the verbs used in the sentences? o they are past tense verbs, which are often used in narrative essays o they are past tense verbs, which are not often used in narrative essays. o they are future tense verbs, which are often used in narrative essays o they are future tense verbs, which are not often used in narrative essays.