diff between env. engi, env studies, sustainable development?

<p>Hey guys, </p>

<p>I was curious as to what the differences between Environmental engineering, environmental studies and sustainable development are? Does Ev. engineering focus more on math/science, env studies on ecology or political science and sustainable development more on innovations???? Also, which is the hardest major in terms of retaining a high GPA?</p>

<p>Thanks!</p>