We are given that \( K \) is algebraically closed and contains a finite field \( F \), and that \( L \) is the subfield of \( K \) consisting of algebraic elements over \( F \).
Step 1: Evaluate S1 (Algebraic closure of \( L \))
Since \( K \) is algebraically closed, the algebraic elements over \( F \) form a subfield that is also algebraically closed. Therefore, S1 is TRUE.
Step 2: Evaluate S2 (Finiteness of \( L \))
Since \( K \) is algebraically closed and contains a finite field \( F \), the field \( L \), being a subfield of \( K \), must be infinite because it contains infinitely many algebraic elements over \( F \). Therefore, S2 is TRUE.
Final Answer
\[
\boxed{(C) \text{ both S1 and S2 are TRUE}}
\]