Which contributes to the lack of evidence of the Period of Heavy
Bombardment on Earth?

The correct answer to this would be:  

Earth’s volcanoes

Together with weathering and plate tectonic movements, Earth’s volcanic eruptions and emission of lava has destroyed/covered many of the craters which were created on Earth during the Period of Heavy Bombardment.

IamSugarBee

The correct answer to this would be letter:  

A. Earth’s volcanoes

Together with weathering and plate tectonic movements, Earth’s volcanic eruptions and emission of lava has destroyed/covered many of the craters which were created on Earth during the Period of Heavy Bombardment.

when [oh-] is 10-5  m, and [h3o+] is 10-9  m, the poh is 5 and ph is 9. again in both cases the sum of ph and poh is 14. however, the hydrogen ion concentration is not always going to be equal to exactly 1 x 10 raised to a negative number. for example, we skipped over the value of 2.0 x 10-7.