Process has been very smooth. we are not confident that it will be completed on time.A.

问题补充：

Process has been very smooth. , we are not confident that it will be completed on time.

A. Therefore

B. Besides

C. Though

D. However

答案：

A. Therefore

B. Besides

C. Though

(答案→)D. However

解析：考察副词辨析。A因此；B而且；C否则，要不然；D然而；句意：过程很顺利，然而，我们很不自信会不会准时完成。根据句意说明D正确。