Unbalanced forces - A
cause the motion of an object to change
B
cancel each other out
C
allow an object to remain at rest
D
are always greater than the force of gravity

it should be d

Explanation:

bc i alredy don that

An unbalanced force is (A)  the cause of motion of an object to change.

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in scientific notation, the value of the  speed of light in a vacuum

  will be written as 2.995 * 10^8. when this value is represented in the form of

  a * 10^b, then, a = 2.995 and b = 8.

the value of the speed of light in a vacuum given above can also be rounded up to approximately 300000000. in this case, the scientific notation will be written as 3 *10^8.