Little
P : that he had been let down
Q : stood by all these years
R : did he realise
S : by a colleague whom he had

The Proper sequence should be:

A. RPSQ

B. RSQP

C. QSRP

D. QSPR

Answer: Option A

Solution(By Examveda Team)

Little did he realize that he had been let down by a colleague whom he had stood by all these years.