Final answer:
The male urethra is housed within the corpus spongiosum, a structure that fills with blood during an erection and allows for the passage of urine and semen. The option a is correct.
Step-by-step explanation:
The structure that houses the male urethra is the corpus spongiosum.
During an erection, the corpus cavernosum and the corpus spongiosum which contains the urethra, fill with blood.
However, it is the corpus spongiosum that surrounds the urethra on the ventral portion, enabling the passage of both urine and semen.
This differentiates it from the corpus cavernosum which is primarily involved in erection and does not contain the male urethra.
The other structures such as the bulbourethral gland, Buck fascia, and the corpus cavernosum do not house the urethra.
The bulbourethral gland is responsible for contributing to the semen volume, Buck fascia is a layer of deep fascia, and the corpus cavernosum are paired erectile tissues that fill with blood to facilitate erection but do not contain the urethra.
Hence, the option a is correct, the male urethra is housed within the corpus spongiosum.