Correct option is B
The correct order is (b)
SQPR.
Formed sentence:
“It was the most interesting book that I had ever read.”
Explanation: We begin with the clause
“It was” (subject + verb), follow with the superlative phrase
“the most interesting”, then the noun + relative marker
“book that”, and finally the defining relative clause
“I had ever read.” This yields a coherent, grammatically correct sentence.