Mr.Smith has been ____in his research for more than 3 hours.

She has been sitting there for more than 2 hours.去掉for可以吗,为什 The research requires more money than has been put in. He has been working for more than 5 hours．________ he is so His grandpa has been _____ (death) for more than ten years. Mr Smith,together with his wife and children,____in Shanghai Mr.Smith ___here for about two hours. Mr.Smith ___here for about two hours.A.has left B.left from My grandfather has been c___matchboxes for more than 20 year (Mr.Smith's passport) has been issued I've been waiting for you for more than two hours I can hard My grenny has been in Beijing for 〔more than/over〕3years The system clock has been set back more than 24 hours