What does the -40, -42, -43, -44, -46,-48 mean for each isotope of Calcium?

21 just playing hshsjsjshsgdhdhdhhd

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.

Sorry i think the answer is b