Directions: For the Assertion (A) and Reason (R) given below, choose the correct alternative. Assertion (A): The Himalayas once lay under the sea. Reason (R): Fossils of marine creatures are found in the Himalayan region.

Introduction / Context:
This question belongs to basic physical geography and geology. It examines the idea that the Himalayan mountain range was once associated with an ancient sea and uses fossil evidence to justify this conclusion. It is a classic example of how scientists use observable clues to reconstruct Earth geological past.

Given Data / Assumptions:

• Assertion (A): The Himalayas once lay under the sea.
• Reason (R): Fossils of marine creatures are found in the Himalayan region.
• We assume standard school geography content about plate tectonics and fossils.
• The question asks if A and R are true and whether R correctly explains A.

Concept / Approach:
Fossils provide crucial evidence for past environments. When marine fossils are found high up in mountain rocks, it suggests that those rocks were once laid down under the sea and later uplifted. In the case of the Himalayas, plate tectonics explains how the collision between the Indian plate and the Eurasian plate uplifted sediments from the ancient Tethys Sea to form the mountains.

Step-by-Step Solution:
Step 1: Evaluate Assertion (A). The Himalayas are known to have been formed from sediments deposited in the Tethys Sea. Over millions of years, these sediments were compressed and uplifted as the Indian plate collided with the Eurasian plate. Thus it is correct to say that the region that is now the Himalayas once lay under the sea.Step 2: Evaluate Reason (R). Geologists have discovered fossils of marine organisms such as shells and other sea life embedded in Himalayan rocks. This is well documented in geography textbooks as a key piece of evidence of the sea origin of these rocks. Therefore R is also true.Step 3: Check whether R explains A. The presence of marine fossils in rocks that are now at high altitudes strongly indicates that those rocks formed in a marine environment and later rose. This directly supports and explains the idea stated in the assertion that the Himalayas once lay under the sea.Step 4: Therefore both A and R are true and R is a correct scientific explanation for A in this school level context.

Verification / Alternative check:
If the Himalayas had never been under the sea, one would not expect to find fossils of marine organisms in rocks there. The match between the type of fossils and the concept of a former sea strongly supports the standard geological explanation. This is exactly how real geologists reason from evidence to conclusion, confirming that the relationship between A and R is explanatory.

Why Other Options Are Wrong:
Option b is incorrect because R clearly does explain A. Options c and d treat one of the statements as false, contradicting well established textbook facts about the Himalayan origin and the presence of marine fossils. There is no support for treating either A or R as false.

Common Pitfalls:
Some students may think the Himalayas have always been mountains and find it hard to imagine them under a sea. Others may know about fossils in general but not connect them with past environments. Remember that fossils are like clues that tell us where and how rocks were formed long ago, especially when found in unexpected places like mountaintops.

Final Answer:
The correct choice is that both Assertion (A) and Reason (R) are true and R is the correct explanation of A.