書名：笛藤新TOEIC必考單字600
頁數：P133 第5題
題目：A supplier who has chronic trouble _____ his obligations to a customer
will quickly lose customers.
(A)fulfill
(B)fulfills
(C)fulfilling
(D)fulfillment
疑問：答案是C,請問為什麼不是B?
謝謝!