Which of the following are true?
I $f(p, q, r)$ has three partial derivatives.
II If $R = F(u, v)$, then $R_u$ means the same as $\frac{\partial R}{\partial v}$.
III If $r = f(s, t)$, then $\frac{\partial r}{\partial s}$ at $(-2, 6)$ is 3 means that when
s is fixed at the value $s = -2$ and t changes from
the value $t = 6$, the output increases by 3.
a) Only I and III are correct
b) Only I is correct
c) None are correct
d) Only II is correct
e) Only II and III are correct
f) Only I and II are correct
g) Only III is correct
h) All are correct