This can also mean: "Their women." That's what I typed and it counted it as wrong. The same word is used for "woman" and "wife" in Greek. Though I understand that when you say "η γυναικα ΜΟΥ" it makes more sense for it to mean "wife" instead of "woman," when ownership is shown like that, I still do not believe the answer I gave should be marked incorrect.
We have "women/wives/ladies" for every use of "γυναίκα" and it is included here as an alternative. Did it say you were wrong or "another correct sentence" or "almost correct"? These do not mean wrong. If you hover over γηναίκα above you'll find at the bottom "women". You have to scroll.
Correct in the plural and for a fuller view go back to Basic 1 and check out the Tips & notes which you'll find on the homepage. There is a good explanation and of other important issues. In fact, you should always read the Tips & notes you'll find lots of useful information.