'Opiate' is a narcotic substance that has mood-altering effects. The passage discusses what works as the opiate of the people and why. Statement A sounds conclusive as an explanation of why people need an opiate. So, it must come last. Now, statement C mentions the full name 'Karl Marx'; so, it must be introductory and come before statement B which mentions 'Marx' only. So, the link is C-B. Now, 'Marx thought religion was the opiate'(B) but television, etc. are 'even more of an opiate'(D). therefore the sequence is CBDA.