Most American colleges and universities use the grading system of A,B,C,D and F.

VOA: special.2009.03.05

Then, your muscle cells would start producing Hepatitis B surface antigen and your immune system recognizing that's a foreign protein would start responding to it.

于是,肌肉细胞将会,开始制造乙肝表面抗原,然后免疫系统就会识别出,那是外来蛋白质并且产生免疫应答

耶鲁公开课 - 生物医学工程探索课程节选