The primary female sex organs are those that are directly involved in reproduction. These organs are responsible for producing gametes and supporting reproduction.
Step 1: Analyzing the options.
- Mammary glands (Option 1): Mammary glands are responsible for milk production and breastfeeding, but they are not the primary sex organs.
- Uterus (Option 2): The uterus is important for nurturing the developing embryo, but it is not the primary organ for producing eggs.
- Ovaries (Option 3): The ovaries are the primary female sex organs. They produce eggs (ova) and secrete hormones like estrogen and progesterone, which are crucial for the reproductive system.
- Cervix (Option 4): The cervix is part of the female reproductive system, but it is not the primary organ for reproduction.
Step 2: Conclusion.
The primary female sex organ is the ovaries.
Final Answer:
\[
\boxed{\text{The correct answer is (3) Ovaries.}}
\]