Question

we know more about space than we do about our own oceans. but why? exploring the deep ocean presents enormous challenges: extremely limited visibility, freezing temperatures, difficulties communicating with the surface... the list goes on and on. but the greatest obstacle to deep sea exploration is the crushing pressure within the oceans depths. at sea level, the air pressure pushing down on us is 14.7 pounds per square inch. because weve adapted to this pressure, we barely feel it. as we travel into space, that pressure decreases. however, the deeper we travel into the ocean, the more pressure our bodies and submersibles must withstand. in challenger deep, the deepest point in the ocean, the pressure is 15,750 pounds per square inch, more than one thousand times the pressure at sea level. thats why it was such an enormous triumph when the vessel trieste reached challenger deep in 1960. the trieste was one of the first bathyscaphes, deep - sea vehicles with steel cabins. designed by august piccard in 1953 to withstand the weight of the water at moderate depths, the trieste was sold to the united states navy in 1958. the navy spent the next two years modifying the vessel ______ before sending it on its triumphant 1960 voyage to challenger deep. fill in the blank in the paragraph with the most logical inference.

Explanation:

The text emphasizes the challenges of deep - sea exploration due to high pressure. The Trieste was initially designed for moderate depths. To reach the extreme pressure environment of Challenger Deep, it needed to be further strengthened to withstand the even greater pressure.

Answer:

to better withstand the extreme pressure at Challenger Deep