Based on SAS help version 4, it should be D: the whole file.

"The SASFILE statement opens a SAS data set and allocates enough buffers to hold the entire file in memory. Once it is read, data is held in memory, available to subsequent DATA and PROC steps or applications, until either a second SASFILE statement closes the file and frees the buffers or the program ends, which automatically closes the file and frees the buffers."