Open circulatory system is present in
I) Arthropods
II) Annelids
III) Chordates
IV) Molluscs
A. III only
B. III and II only
C. IV only
D. I only

Hint: As we know that every organism has a unique circulatory system for blood transportation. It can be of two types including open circulatory system where blood moves outside the blood vessels in open spaces called sinuses and closed circulatory system where the blood is confined to within definite vessels.

Complete answer:
As we are very well aware about the circulatory systems in chordates and non- chordates that help in transporting blood to every part of the individual’s body. There are basically two types of circulatory systems.
The first one is a closed circulatory system where the blood is confined within definite blood vessels. This type of circulatory system is found in Annelids, Cephalopod Molluscs, Echinoderms and vertebrates.
The second one is an open circulatory system where the blood moves outside the blood vessels in open spaces called sinuses. It is also called the Lacunar type of circulatory system. It is found in Arthropods, Non-cephalopod Molluscs, Hemichordates and Urochordates.
The blood is pumped by the heart into the body cavities called hemocoel where the tissues are surrounded by the blood. And these organisms typically have a relatively high volume of haemolymph and low blood pressure.
Option (A) is incorrect because not all chordates have an open circulatory system, Vertebrates have a closed circulatory system.
Similarly not all Molluscs have an open circulatory system.

Therefore, from the above explanation the correct answer is (D).

Note:
Remember that a closed circulatory system is better than the open type because blood moves faster in a closed system so it is more efficient and the oxygenated and deoxygenated blood does not get mixed. Different organs receive a variable amount of blood according to their needs which is provided better by a closed circulatory system.