An airplane is flying west at 200 km/h two hours later it is flying west at 3000km/h its average acceleration is 6m/s2

the answer to your question is:

c. complementary base-pairing

which

what is a measurement of the earth’s history divided into time periods?

> fossil record <

sedimentary rock

> geologic time scale <

radioactive elements

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.

you're crazy : )