as platform, as a platform

Polar bears live mainly on _____ sea ice, which they use as ____ platform for hunting seals.
This was one of China's university admission examination questions. The given answer is: "no article...a".
I'd like to know whether 'the' is all right for the first blank and 'no article' for the second.
Thank you very much.

I think you can use "the" with the first. As to "platform", I am inclined to say you could omit "a" but it reads better with it.