Heart of controlled trial is -

Ans. is 'c' i.e., Randomization * Randomization is the heart of RCT.* Randomization is a statistical procedure by which the participants are allocated into study group (in which intervention is given) and control group / reference group (in which intervention is not given).* It is worth noting that randomisation is done while dividing the participants into study group and control (reference) group, and not while selecting subjects for study, i.e. randomization is done after the sample of subjects has already been selected.* Therefore, each participant has 'equal and known chance' of falling into either study group or control group.* Randomization is an attempt to eliminate bias and allow comparability.* It will give the greatest confidence that the groups are comparable so that "like" can be compared with "like".* It ensures that the investigator has no control over allocation of participants to either study or control group, thus eliminating what is known as selection bias.* That means, by random allocation, every individual gets an equal chance of being allocated into either group, study (experimental) group or control (reference) group.