Question

read the passage. then answer the question. mapping the ocean floor before the 1900s, people were not certain what the ocean floor looked like. they could only measure the depth in one spot at a time, by dropping a weighted line into the water. by the 1920s, people were using sonar, a technology that measures how long a sound wave takes to bounce back from the ocean floor. scientists discovered deep - sea trenches and mid - ocean ridges. in the 1960s, the navy began using sonar to map several paths at one time. computers combined the results to create a picture of an area. scientists also towed sonar deep beneath. read this sentence from the passage. before the 1900s, people were not certain what the ocean floor looked like. which text evidence supports this idea? a scientists discovered mid - ocean ridges. b computers created a picture of an area. c people could only measure water depth. d people explored underwater canyons.

Explanation:

The text states that before the 1900s people could only measure the depth in one spot at a time by dropping a weighted line. This shows their limited knowledge of the ocean - floor as they could only measure water depth and not map the overall ocean - floor. Options A and B are about later technological advancements and discoveries, and option D is about exploration which is not related to the limited knowledge before the 1900s. Option C directly supports the idea that before the 1900s people were not certain what the ocean - floor looked like because they could only measure water depth.

Answer:

C. People could only measure water depth.