Answer the following question given this paragraph: 

Studying the ocean floor is difficult because the environment is so hostile. The seafloor can be studied indirectly with tools such as sonar. It can be studied directly using special vehicles. Some vehicles carry scientists and their devices to the ocean floor. Other vehicles are operated remotely.


Q: What tool is useful for studying the ocean floor because the environment is remote and underwater?

 Choices:

- microscope

- telescope

- scale

- sonar

A:
sonar
