Antony conducts a correlational study and finds that students who work more hours in part-time jobs have higher grades. what antony doesn't know is that both of these phenomena are caused by students' motivation levels. this is an example of

the answer is: the third variable problem
the third variable problem refers to the additional factor that could mistakenly lead to the false conclusion in determining the causal relationship between two other factors.
Other example:
There was a study that shown that eating soy bean leads to the development of breast cancer. But if we take a look at East Asian population who consume more soy beans compared to western people, East Asian population have far less cancer cases.
In this case, we can say that Genetic is a third variable problem