Thanks for that link. It made the problem easy. You need to satisfy two conditions: c<=a OR c<=b since the problem specified that ONE container held the desired quantity (if the quantity could be split across both containers then I guess this would be a much harder problem). The other condition is that c must be an integral multiple of gcd(a, b).

My solution in lisp:

(defun fillable (a b c)
    (cond ((and (> c a) (> c b)) nil)
        ((zerop (rem c (gcd a b))) T)
        (T nil)))

(defun cases (n)
    (cond ((zerop n) nil)
        (T (if (fillable (read) (read) (read))
               (format t "YES~%")
               (format t "NO~%"))
           (cases (1- n)))))

(cases (read))