The passwd binary has an special permission instead of the execution permission for the owner. What does it mean?

$-$rwsr$-$xr$-$x $1$ root root $59976$ Nov $2408$:$05/$bin$/$passwd

a$.$ That the resulting process has an effective UID of $0$

b$.$ That the binary file has an ACL with further permissions

c$.$ That the binary is secured from tampering

d$.$ That the resulting process has an effective UID matching the user executing the binary