Exploration of antarctica’s interior did not begin until
a) tractors were brought to the continents

b)sailors from european countries landed on pack ice

c)a treaty was signed by 12 nations

d)airplanes were strong enough to withstand the winds and cold

I think the answer is d)airplanes were strong enough to withstand the winds and cold.

It was difficult to travel through ship because of the climate and geographical conditions in Antarctica. They had to travel using good aircrafts that can handle strong and cold winds. Machines were also used to explore the area.

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