Advanced biology students, for example, trekked tothe Black Rock Forest, in Orange County, N.Y., to measure snow depth, andfrequented the Museum of Natural History.
A language can't be treated like a subject in school such as history or biology; in the real world you cannot 'fail' when you make a certain number of mistakes.
The association should be coherent; that is, plausible and explicable biologically according to known facts in the natural history and biologyof the disease.