[A] : Annelids , Arthropods and mollusks are protostomial coelomates .
[R] : They all show bilateral symmetry , tube with in tube body plan and three germ layer derivations.

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

To solve the question, we need to analyze both the assertion (A) and the reason (R) given in the statement.

### Step 1: Understand the Assertion (A)
The assertion states that "Annelids, Arthropods, and mollusks are protostomial coelomates."
- **Explanation**:
- Annelids (segmented worms), Arthropods (insects, arachnids, crustaceans), and Mollusks (snails, clams, squids) are all part of the group known as protostomes.
- Protostomes are characterized by their embryonic development where the mouth forms before the anus.
- They also possess a true coelom, which is a fluid-filled body cavity.

### Step 2: Understand the Reason (R)
The reason states that "They all show bilateral symmetry, tube-within-tube body plan, and three germ layer derivations."
- **Explanation**:
- Bilateral symmetry means that the body can be divided into two equal halves along one plane.
- The tube-within-tube body plan refers to the organization where there is an outer body wall and an inner digestive tube.
- Three germ layers (ectoderm, mesoderm, endoderm) indicate that these organisms develop from three primary layers during embryonic development.

### Step 3: Determine the Relationship between A and R
- Both A and R are true statements.
- The reason (R) provides a correct explanation of the assertion (A) because the characteristics mentioned in R (bilateral symmetry, tube-within-tube body plan, and three germ layers) are indeed features that support the classification of Annelids, Arthropods, and Mollusks as protostomial coelomates.

### Conclusion
Both the assertion (A) and the reason (R) are true, and R correctly explains A. Therefore, the correct answer is:
- **Option A**: Both A and R are true, and R is the correct explanation of A.

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