To determine where the circulatory system is present, we need to analyze the options provided in the question.
### Step-by-Step Solution:
1. **Understanding the Circulatory System**: The circulatory system is a complex network responsible for transporting nutrients, gases, hormones, blood, and waste products throughout the body. It is typically found in more complex organisms.
2. **Evaluating Option 1 - All Diploblastic Animals**: Diploblastic animals, such as cnidarians (jellyfish, corals), have only two germ layers (ectoderm and endoderm) and lack a true circulatory system. Instead, they rely on diffusion for nutrient and gas exchange. Therefore, this option is incorrect.
**Hint**: Diploblastic animals have limited body structures and rely on simple diffusion rather than a circulatory system.
3. **Evaluating Option 2 - All Triploblastic Animals**: Triploblastic animals have three germ layers (ectoderm, mesoderm, and endoderm). While many triploblastic animals do have a circulatory system, not all do. For instance, some invertebrates like flatworms lack a true circulatory system. Hence, this option is also incorrect.
**Hint**: Not all triploblastic animals possess a circulatory system; some may have alternative methods for transport.
4. **Evaluating Option 3 - All Protostomians**: Protostomians include a wide range of animals such as arthropods, mollusks, and annelids. While some protostomians have a circulatory system, many lower invertebrates do not possess a true circulatory system. Thus, this option is incorrect.
**Hint**: Consider the diversity within protostomians; not all have developed circulatory systems.
5. **Evaluating Option 4 - All Deuterostomians**: Deuterostomians include animals such as echinoderms and chordates (which include humans). Most deuterostomians possess a well-developed circulatory system. Since humans, as deuterostomians, have a complex circulatory system, this option is correct.
**Hint**: Deuterostomians generally have more complex body structures, including a circulatory system.
### Conclusion:
The correct answer is **Option 4 - All Deuterostomians**.
