单项选择题
Kieselguhr G consists of natural kieselguhr that has been extracted with hydrochloric acid and calcined，and to which adout 15% Of calcium sulphate hemihydrate has been added.上文中，“which”指代（）
A．natural kieselguhr
B．calcined kieselguhr
C．hydrochloric acid extracted Kieselguhr
D．Kieselguhr G
E．Calcium sulphate hemidydrate