Answer
We can rank the loops according to the magnitude of $~~\int~B \cdot ds~~$ around each loop:
$(c) = (d) \gt (b) \gt (a)$
Work Step by Step
$\int~B\cdot ds = \mu_0~i_{enc}$
Loop $a$ encloses the smallest amount of current $i_{enc}$.
Loop $b$ encloses the second smallest amount of current $i_{enc}$.
Loop $c$ and loop $d$ enclose the same amount of current $i_{enc}$
We can rank the loops according to the magnitude of $~~\int~B \cdot ds~~$ around each loop:
$(c) = (d) \gt (b) \gt (a)$
