There is a desk that can hold at most four (4) files. On this desk, six (6) files A through F are used for a job. When the fifth file needs to be put on the desk, the file with the longest time since the last use among the four (4) will be put in a drawer. If the files are put on the desk and referenced in order of A, B, C, D, E, C, B, D, F, B, which of the following is the last file to be put in the drawer?