Some group (G, o) is known to be abelian. Then, which one of the following is true for G?

The transitive closure of the relation
$$\left\{ {\left( {1,2} \right)\left( {2,3} \right)\left( {3,4} \right)\left( {5,4} \right)} \right\}$$
on the set $$A = \left\{ {1,2,3,4,5} \right\}$$ is ________ .

The complement(s) of the element 'a' in the lattice shown in Fig. is (are) ........... .