What does sustainability mean as it is used in this sentence from "The Ride of His Life"?

He focuses his research and life's work on marine resource
sustainability

A. action of converting waste into reusable material

B. surroundings in which a person or animal lives

C. process by which organisms use sunlight to create food

D. ability to be maintained at a certain rate or level

in other words

to put it differently

for one thing

as an illustration

in this case

for this reason

to put it another way

that is to say

with attention to

by all means

important to realize

another key point

first thing to remember

most compelling evidence

must be remembered

point often overlooked

to point out

on the positive side

on the negative side

with this in mind

notably

including

like

to be sure

namely

chiefly

truly

indeed

certainly

surely

markedly

such as

especially

explicitly

specifically

expressly

surprisingly

frequently

significantly

particularly

in fact

in general

in particular

in detail

for example

for instance

to demonstrate

to emphasize

to repeat

to clarify

to explain

to enumerate

answer: a lonely woodcutter comes by and decides to chop down the tree, while chopping, connor murphy took a nap next to the tree. waking up from the sound of chopping, he notices the tree falling on him. unable to escape, connor get hit and dies. this was the last of him.

b is the answer.   i sat on the lumpy sofa, totally exhausted, with a bad taste in my mouth, wondering what i should do next.