Select the three words in the following sentence that indicate it is in the third person. He thought about writing a letter, but he knew his friends might not get it in time.

Astronomers studying the planet of rhombus have detected sedimentary rock on its surface. one astronomer wonders if material in this sedimentary rock used to be in igneous rock deep in rhombus’s interior. can igneous rock become sedimentary rock? explain your answer.