【单选题】

Questions 147-149 refer to the following letter.

Dear Sirs,
Two weeks ago, I sent you an order for 45 copies of the "ContemporaryEnglish" dictionary, (147) the importance of swift delivery. They should have arrived last week at the latest when the new semester was due to begin.
I have received no acknowledgement of the order, nor have the dictionaries (148) .
Failure to receive them on time is causing serious inconvenience.
I shall be glad if you look into this matter as soon as possible and let me know (149) .they may be expecteD、
A、what
B、when
C、which
D、whom