Answer:
The correct answer is - variables that they didn't control and not enough replicates
Step-by-step explanation:
In this particular case, Pablo and Johanna using too many variables in their experiment or research, All the variables used, are not controlled and with time these variables can not be replicated again on experiment groups.
They did not select a particular age or weight of dogs, the diets are different and they feed dry kibble to only one dog. There are so many variables and for a better result experiment, all variables should be controlled only the independent variable is permitted to manipulate.