Question

outi tervo and team studied the effect of human - caused noise on narwhals (monodon monoceros), arctic marine mammals that are sensitive to acoustic changes in their environment. hypothesizing that elevated sound levels affect foraging among narwhals, tervos team compared narwhal diving behaviors in natural sound conditions with those behaviors in two human - caused sound exposure conditions—ship sounds and ship sounds coupled with sonic pulses. both exposure conditions resulted in significant decreases in the number and target depth of deep dives (associated with foraging) relative to natural conditions. however, differences between diving behaviors in the two exposure types were negligible, a finding that could be attributed to the fact that
which choice most logically completes the text?
a. narwhals forage at shallower depths in the presence of ship sounds alone than in the presence of ship sounds coupled with sonic pulses.
b. sonic pulses can be heard at significantly greater ocean depths than ship sounds can.
c. the narwhals weren’t as sensitive to human - caused sounds as the researchers had predicted.
d. ship sounds contribute so much to the overall sound level that the addition of sonic pulses has little effect on the narwhals’ auditory environment

Explanation:

The text is about a study on the effect of human - caused noise (ship sounds and sonic pulses) on narwhals. The key is to find the option that logically completes the text regarding the reason for differences in diving behaviors.

• Option A: If narwhals forage at shallower depths in the presence of ship sounds alone than in the presence of ship sounds coupled with sonic pulses, it can explain the differences in diving behaviors (related to foraging depth).
• Option B: Sonic pulses being heard at greater ocean depths than ship sounds doesn't directly explain the difference in diving behaviors between the two human - caused sound exposure types.
• Option C: Narwhals not being as sensitive to human - caused sounds as predicted doesn't address the difference in behaviors between the two sound exposure scenarios.
• Option D: Ship sounds contributing less to the overall sound level (with the addition of sonic pulses having little effect) doesn't explain the difference in diving behaviors related to the two sound exposure types.

Answer:

A. narwhals forage at shallower depths in the presence of ship sounds alone than in the presence of ship sounds coupled with sonic pulses.