The sea floor is mapped using echolocation​

Echo sounding is the key method scientists use to map the seafloor today. The technique, first used by German scientists in the early 20th century, uses sound waves bounced off the ocean bottom. Echo sounders aboard ships have components called transducers that both transmit and receive sound waves.

the letter score 3 in structure because, the letter includes some requirements for a business letter.

the letter scored 1 in tone because,  the tone and vocabulary are threatening and negative. the request is unreasonable.

the diary, textbook, and interview are all primary sorces and the scholarly journal is a secondary sorce.