4. (2002 Anhui Province Competition Question) A tetrahedron has three lateral faces, two of which are isosceles right triangles, and the other is an equilateral triangle with a side length of 1. Therefore, the volume of this tetrahedron ( ).
A. has a unique value
B. has 2 different values
C. has 3 different values
D. has more than 3 different values
(3) As shown in Figure (3), if $S A=S B=A B=A C=B C=1, S C=\sqrt{2}, S A \perp A C, S B \perp B C$, then $V_{S-A B C}=V_{A-S B C}=$ $\frac{\sqrt{2}}{12}$.
4. Choose C. Reason: By taking specific simple numbers for the edges and base of the tetrahedron and performing specific calculations to explore.
(1) As shown in Figure (1), if $S A=S B=S C=B C=1, S A \perp S B, S A \perp S C$, then $V_{S A B C}=V_{A-S B C}=\frac{\sqrt{3}}{12}$;
(2) As shown in Figure (2), if $S B=S C=B C=1, S A=\frac{\sqrt{2}}{2}, S A \perp A B, S A \perp A C$, then $V_{S A B C}=\frac{\sqrt{2}}{24}$;