Hiroki's mom is worried he is not saving enough. She says he should save some money for an emergency. He says he can use his credit card in an emergency. Who is right?

The son is right.

Explanation: With the credit card you can use it for what ever you even if you don’t have money on it.  With a credit card you will be able to pay it back.

Hirokis mom

Explanation:Because a mom is doing what is best for a child and she doesn't want her son to spend all his money on a credit card

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.