据此判断其中酸性最强的是( )
A:血浆
B:唾液
C:胃液
D:尿液
— Look, she is our new doctor.
— No, I don't.
长方体ABCD-A1B1C1D1中,AB=BC=4,E为A1C1与B1D1的交点,F为BC1与B1C的交点,又AF⊥BE,则长方体的高BB1等于( )