一口水井，在不会渗水的情况下，A抽水机用4小时可将水抽完，B抽水机用6小时可将水抽完。现用A、B两台抽水机同时抽水，但由于渗水，结果用了3小时才将水抽完。那么在渗水的情况下，用B抽水机单独抽，需要几小时抽完？（ ）

A.30

B.45

C.60

D.72

A.540

B.580

C.600

D.640

A.56

B.64

C.80

D.120

A.20

B.30

C.40

D.50

A.3/10

B.2/5

C.1/2

D.3/5

A. an; the

B. the; a

C. the ;/

D. / ; a

A. writing

B. to write

C. written

D. being written

A. In reply to

B. In addition to

C. In charge of

D. In place of

A. to find

B. found

C. finding

D. having found

A. Unless

B. Although

C. Before

D. Once