Concept:
Shankaracharya is the chief philosopher of Advaita Vedanta.
Advaita Vedanta teaches non-dualism.
According to this philosophy:
\[
\text{Brahman alone is ultimately real}
\]
Step 1: Check Assertion (A).
Shankaracharya considered the world as appearance from the ultimate standpoint.
The world is not absolutely real like Brahman.
So, Assertion (A) is correct.
Step 2: Check Reason (R).
The Reason says that Brahman is the only absolute reality.
This is the central doctrine of Advaita Vedanta.
So, Reason (R) is correct.
Step 3: Check explanation.
Because Brahman alone is absolutely real, the empirical world is considered appearance.
Thus, Reason correctly explains Assertion.
Hence:
\[
\boxed{\text{(A)}}
\]