说明
In joy or in sorrow, my brother plods away at his lessons until he learns. 不论是在欢乐时还是在悲伤时，我弟弟都孜孜不倦地读书，直到学会为止。
请做下面的英语试题：
____ it or not, his discovery has created a stir in scientific circles. A. Believe B. To believe C. Believing D. Believed(全国四级,97.1-49)