When blood flows into the cylinders of the penis causing it to become hard

When blood flows through the penis, this causes the penis to have an erection. Erections occur when a male gets "sexually excited" and this allows the blood to flow through. Sometimes, erections can happen for no reason at all but this usually happens way more during puberty.

since you have not provided the options here i   am going to give you general overview about hormone.hormone are actually the part of endocrine system in our body and produced by the endocrine glands. the hormones act like a chemical messenger   within human body. once produce by the glands they   travel through the blood stream and reach at specific or target tissue and organs   which result in control of our body function. the hormones are specific in their work and work on only the targeted tissue or organ   . with the of hormone endocrine system regulate the heart rate , metabolism, our mood and   growth as well as the development and even the sleeping cycle etc. they actually are the messenger for body cell and organs .

doing something can distress you in any way you can