A binary relation $$ is

Reflexive if for every $,$

Symmetric if for every $$ and $,$ implies $$

Transitive if for every $,,$ and $,$ and $$ implies $$

Which of the following is symmetric and transitive, but not reflexive?

a$.$

$\{(,),(,),(,),(,),(,),(,),(,)\}$

b$.$

$\{(,),(,),(,),(,),(,),(,)\}$

c$.$

$$