It’s D the time period within pendulums are constant, distance is always measured with kilometers within cities and basic unit is always seconds.
Answer: It leads to a front. A front is.., I don't know how to explain it, so I'll add a picture. Fronts are made out of clouds and usually bring rain. So the answer is C: The formation of clouds and rain.
Explanation:
Sometimes it just picks for you
A car speeds up on how its built