Answer:
A
Step-by-step explanation:
A population is a group of the same organism living in a particular area - in this case, it's the total number of brook trout in the pond.
B is wrong because it is not proportion. Proportion refers to a part of a whole, and in this problem, we want the whole thing.
C is wrong because it's not a sample. Again, sample is similar to proportion in that it's only a small group out of the big group - not what we're looking for.
D is wrong because it's not the population of fish. Fish is really broad and general and can include populations of other fish species like tuna or goldfish. We only want brook trout.
Thus, the answer is A.
Hope this helps!
