I ________ letters this morning and ________ for four hours so far．
A.will write; wroteB.have written; have writtenC.was writing; wroteD.have been writing; have written在线课程D
该题考查现在完成进行时和现在完成时。题意为我今天早上一直在写信，到目前为止已经写了4个小时。