When the radius of blood vessels decreases, it causes an increase in resistance to blood flow. According to Poiseuille`s law, resistance is directly proportional to the length of the vessel and the viscosity of blood, but inversely proportional to the fourth power of the radius of the vessel. Therefore, as the radius decreases, the resistance increases.

According to the relationship between blood pressure, cardiac output, and resistance (known as the Ohm`s law for blood flow), blood pressure is directly proportional to cardiac output and resistance. Since resistance increases when the radius decreases, and assuming cardiac output remains constant, the blood pressure will also increase. Therefore, when the radius of blood vessels of a person decreases, their blood pressure will increase.

Option 1, which states that the blood pressure will increase, is the correct answer.