Gun control is a subject ________ Americans have argued for a long time. (2009 .陕西)
. —Who______ it be that is knocking at the door? —It ______ be Father, but I’m not sure.
. . The day________ he was looking forward________ in the end.
. .---Who ________ it be that is knocking at the door? ---It________ be Mother, but I’m not sure.
. .If you cheat in the exam, you could hardly________ it.
. .He once studied in Zhejiang University, ________he went abroad for further study.