Answer is b hope this helps
Definitely D. The brakes on a bike rub against the wheel. Not sure about the others.
It makes the data thet they collect more reliable so if they need the data again, they have already tested it a few times so therefor they know that it is right.
Answer:
Explanation:
so a mechanical wave transfers energy through a medium but unlike other waves that move through very long distances
the distance of the mechanical wave is different
Answer : Yes, distance measurements based on the speed of light used for objects in space.
Explanation : A light year is measurement of distance that light travel in a one year.
In a one year light travels 9460000000000 kilometer.
We know that, speed of light is 
and time is 31536000 seconds in 1 year
so, distance = speed of light X time
Now, the light year is 
Example : The nearest star to earth is about 4.3 light year away.