To answer this question correctly, we need to evaluate the facts around each statement individually before making a comparison:

Statement I: The presence or absence of hymen is not a reliable indicator of virginity.

This statement is true. The hymen is a thin, elastic membrane located at the entrance to the vagina. Contrary to common belief, the hymen is not an impermeable barrier that is always torn when virginity is lost via sexual intercourse. It can vary greatly in shape and size from person to person. Some girls are born without a hymen, some have small hymenal tissue, and others have hymens that are very elastic. Moreover, the hymen can be stretched or torn during a variety of non-sexual activities such as tampon use, physical exercise (e.g., biking, gymnastics), or medical examinations. Therefore, the state of the hymen is not a definite indicator of virginity, making statement I true.

Statement II: The hymen is torn during the first coitus only.

This statement is false. As previously mentioned, the hymen can be stretched or torn by activities that are not sexual in nature. Additionally, many women may not experience tearing of the hymen at all during their first sexual intercourse. In cases where the hymen is more elastic or resilient, it may not tear during sexual activity. Furthermore, there are practices and surgeries, such as hymenoplasty, that can restore or create a hymen-like structure, indicating that the hymen can be altered multiple times throughout a woman's life. Thus, the claim that the hymen is torn only during the first coitus is incorrect.

Based on the explanations provided:

Option C (Statement I is true but Statement II is false) is the correct answer.