Answer: ca is true since given any pair of vertices $v_k$ and $v_l$ where $k \neq l$, either $k < l$ or $l < k$. This implies that ${v_k,v_l} \in E$ or ${v_l,v_k} \in E$, which mean the same thing since ${v_k,v_l} = {v_l,v_k}$. Therefore this means that for any pair of vertices, there exists an edge that connects said pair. This is the definition of any complete graph. b is also true since any complete graph is connected. This means that the answer is c.
Answer: ashortest paths:${v_1,v_5 },{v_5,v_3 }$ with a path length of 3,
${v_2,v_1 },{v_1,v_4 }$ with a path length of 5,
${v_4,v_1 },{v_1,v_5 },{v_5,v_3 }$ with a path length of 6,
Answer: c
I is not true since $v_1$ and $v_5$ have an odd degree. But since these two are the only vertices with odd degrees, it has an Euler path making II true. If ${v_1,v_5}$ is removed from the graph then all edges will have an even degree making III true.
Answer: b