a researcher wishes to use an observational study to determine the proportion of drivers who do not stop at a stop sign, depending on how much traffic is in the area at the time. the researcher stays hidden, using cameras and sensors, during times when traffic is light and when it is heavy. after observing for two weeks and analyzing the data, the researcher discovers that drivers stop at stop signs 95% of the time when the traffic flow is heavier than one car per minute. he concludes that an increase in traffic flow causes drivers to stop at stop signs. is it correct for the researcher to draw this causation between traffic flow and whether drivers stop at stop signs? a: yes, he is correct, because the number of drivers who do not stop at stop signs increases as the traffic flow lightens.b: yes, he is correct, because the heavier the traffic flow, the more likely the driver is to stop at a stop sign based on the proportion 95%c: no, he is incorrect, because the researcher used an observational study, and therefore no causation can be drawn.d: no, he is incorrect, because the study was only conducted by one researcher