All my points to who answers this
read the sentence and answer the question.

since the late 1970s, many astronauts have held advanced degrees this education has been useful for mission specialists.

which correctly shows where a semicolon is needed in the sentence?

a.
since the late 1970s, many astronauts have held advanced degrees; this education has been useful for mission specialists.

b.
since the late 1970s, many astronauts have held advanced degrees this education has been useful; for mission specialists.

c.
since the late 1970s; many astronauts have held advanced degrees this education has been useful for mission specialists.

d.
since the late 1970s, many astronauts have; held advanced degrees this education has been useful for mission specialists.