Open circulatory system is present in `underline(("i"))` and `underline(("ii"))`. Fill the correct option for (i) and (ii)

Options

A. `"(i)-platyhelminthes (ii)-molluscs"`
B. `"(i)-arthropods (ii)-echinoderms"`
C. `"(i)-annelids (ii)-arthropods"`
D. `"(i)-arthropods (ii)-molluscs"`

Explanation

To answer the question regarding which organisms have an open circulatory system, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Open Circulatory System**:
- An open circulatory system is characterized by the absence of blood vessels. Instead, blood (or hemolymph) is pumped by the heart into open spaces called sinuses or hemocoels.

2. **Identify Organisms with Open Circulatory Systems**:
- The two major groups of organisms that exhibit an open circulatory system are arthropods and molluscs.

3. **Examples of Organisms**:
- For **(i)**, we can fill in "arthropods". This group includes insects such as cockroaches, crabs, and spiders.
- For **(ii)**, we can fill in "molluscs". This group includes snails, octopuses, and clams.

4. **Final Answer**:
- Therefore, the correct options are:
- (i) Arthropods
- (ii) Molluscs