Section 125 of the CPC - Grounds for Maintenance

A student of mine always asks about this one, and I must admit, I initially got it wrong. Here's the MCQ:

Who can file an application for maintenance under Section 125 of the CPC?

A) Wife B) Child C) Husband D) In-laws

My wrong answer was A) Wife, and I thought to myself, "arrey, kya hoga? Wife will always get maintenance, nahi?" But, of course, the answer is not that straightforward.

**Can you give the correct answer and explain why?