Aresearcher would like to determine the effect of caffeine on memory. participants are randomly assigned to receive a caffeine pill or a sugar pill. both groups complete a recall task that assesses their memory. however, even those who received the sugar pill had a small increase in memory. this is likely due to: a. the experimental effectb. the correlational approach to the studyc. the placebo effectd. the participants becoming smarter

(C) The placebo effect

Explanation:

 The placebo effect is one of the type of treatment that is specifically designed for control all the therapeutic values and this effect is basically works on the various types of symptoms that is generated by our brain.  

It includes the various types of procedures, inert injections and the tablets. The researcher utilized various types of placebo effect controlling system so that they can easily assess our memory.

 According to the given question, the given situation is due to the placebo effect as they can easily determine the quantity of caffeine in the memory.

Therefore, Option (C) is correct.