Helps scientist study our universe and galaxies. A.) Past observations made early in history
B.) Microscopes
C.) Telescopes and space probes
D.) both a and c

D.) both a and c

Explanation:

Past observations made early in history as well as telescopes and space probes are very important in studying our universe and galaxies.

Microscopes are not used in galactic studies. They are only used to study the world of micro-organisms.

d.

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