Correct the mistakes in the following sentences if there is any, and tell which one of the above usages accounts for the tense used in each sentence. (1) The delegation arrives in Shanghai this afternoon. (2) If anyone will call, just tell them I’m not in the office. (3) London is sitting on the Thames. (4) I am declaring this exhibition open. (5) I sometimes stay up till midnight. (6) The exhibition will open on April 1 and close on April 30.