What does the cell membrane let in an out

The cell membrane is semipermeable or selectively permeable. This mean that certain materials may enter and exit  but not others. Water , carbon dioxide and oxygen.

Variables,control,conclusion and finally scientific theory

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.