21. When _____ our order, we s tress ed tha t prompt delivery was of special importance because we had a ssured our customers that we could complete the order by the end of August .
(A)to place
(B)placed
(C)pl acing
(D)place。

答案：登入後查看
統計： A(1), B(0), C(6), D(2), E(0) #2142934