Given below are four parts of a sentence which are jumbled. Pick the option that gives their correct order to make a grammatically correct, meaningful sentence.
A. students were expected
B. studied in earlier classes
C. having reached higher classes
D. to know the formulas and principles

Correct option is D

Option (d) CADB is the correct order of the given sentence.
Final Reconstructed Sentence:
Having reached higher classes, students were expected to know the formulas and principles studied in earlier classes.
Explanation of sentence structure:
C (having reached higher classes): Starts the sentence with a participial phrase showing condition or timing.
A (students were expected): Main subject and verb.
D (to know the formulas and principles): Purpose or expectation.
B (studied in earlier classes): Describes which formulas/principles.
Why this order is correct:
The sentence begins with a perfect participle (C), followed by main clause (A), then infinitive purpose (D), and qualifier (B).
The logical flow moves from cause ➝ subject ➝ expectation ➝ detail.