[填空题]______(既然我们学完了这门课程) , we shall start doing more revision work.

Researchers report that doing two or more things at once may decrease efficiency and actually take extra time switching from one task to another. In the most severe cases, it can even mean the difference between life and death.
"People get tired when they’re trying to multitask(多任务化) ," and in some cases a person could ultimately create more work for himself, according to one of the lead authors, David Meyer, of the university’s psychology department.
The researchers found that time was lost in just switching from one task to another, and that time costs increased with the complexity of the tasks. The subjects got "up to speed" faster when they switched to tasks that were familiar.
When people, say, juggle browsing the Web and using other computer programs, or talk on the phone while driving, they are using their "executive control" processes in their brain, the re searchers said. Those processes can be likened to
A. Because they get tried.
B. Because they are not professional.
C. Because they don’t have the ability.
D. Because they don’t want to do.