Mechanical waves that travel through

a.
a vacuum

b.
outer space

c.
a black hole

d.
a medium

d.  a medium

Explanation: Mechanical waves are waves are oscillations of matter and thus transfer energy through material medium unlike electromagnetic waves which do not require material medium to propagate.

Mechanical waves may be longitudinal or transverse waves.

Sound waves are example of mechanical waves and thuds cannot travel in vacuum whereas light is an electromagnetic wave which can travel in vacuum.

right

explanation:

the population of unionid mussels in the hudson river decreased after zebra mussels were introduced. zebra mussels, a nonnative species, competed with the unionid mussels for food. the zebra mussels were able to outcompete the unionid mussels, allowing the zebra mussel population to increase dramatically over six years. the unionid mussel population decreased due to a lack of food.

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