The strategy of “island hopping" in the Pacific, which was developed by a joint US
ArmyNavy command, involved Allied attacks on what?

Islands.

Explanation:

During the second world war, the US Navy attacked the Japanese by strategically taking islands the Japanese held. This was known as Island Hopping. Once an enemy island was taken, a base would be established or an old enemy base would be renovated to become a strategic position against the Japanese.

the answer is:

c. economic output

productive most commonly means: achieving or producing a significant amount or result.

explanation:

productive can also mean:

these depend on how the word productive is used. most likely productive will mean   achieving or producing a significant amount or result.