The correct option is B distribution of absorbed nutrients
Cockroaches have an open type circulatory system, which means that the blood is pumped by heart and it flows in body cavity directly. The body organs are flooded with blood and they get nutrition directly from here as the blood is present throughout the body. Therefore, the principal function of blood vascular system in cockroach is the distribution of absorbed nutrition.
The oxygen is not distributed by the blood. It is the function of an entirely independent closed type of respiratory system where the oxygen need not to be sent to the blood.
The cockroaches are cold blooded insects, therefore the blood would not either transport the heat to the body.
The transportation of enzymes is directly released in the digestive system of cockroach and they need not to be sent in the blood for its transport.