Please choose the correct ending to complete the given sentence: Health: [header] How to recognize male infertility [title] Understand that male infertility often has no obvious signs. [step] Many infertile men experience a regular sex life and have sperm that looks fine to the naked eye. In this sense, it is difficult to recognize the physical symptoms of male infertility.

Ending1: Warning signs are rare, but some infertile men have lumps or swelling near the testicles, breast growth, erectile dysfunction, and respiratory problems. [title] Feel for a lump or swelling in your testicles. Ending2: External factors such as age, gender, and physical impairment are unavoidable. [substeps] Men who have not had a regular sex life, more directly, may develop an infertility related to a gender trait, such as wanting to have sex for many reasons, or genetics dating back to childhood. Ending3: As a result, it's not uncommon for male infertility to manifest and become visible without noticeable problems. However, keep in mind that there are some fairly minor symptoms that occur during and after menstruation, but they are virtually invisible due to their abnormalities. Ending4: However, it is much more important to have a good sense of something clear for the witness and a close, knowledgeable partner who knows exactly what is going on. Men are most likely fertile in the 60s or earlier.

Answer format: ending1/ending2/ending3/ending4