Question

undersea mining is difficult mainly because: *
the minerals are too light
the ocean floor is hard to reach and work in
it produces too many gemstones
it only yields nonmetallic minerals

Explanation:

Undersea mining faces challenges due to the depth and harsh conditions of the ocean floor. Reaching and operating in such an environment is complex. The other options are incorrect: minerals' weight isn't a main issue; gemstones are not a problem - related factor; and it doesn't only yield nonmetallic minerals.

Answer:

The ocean floor is hard to reach and work in