the other guy is totally wrong. the answer is a for sure. C is showing a covalent bond between 3 atoms. Metals bond differently. Like shown in a and b. However b is innacurate because it shows the electrons being the largest(since they are negatively charged and there is a - sybmol), and we all know protons are much larger than electrons. SO a is correct because it depicts the positive protons(+ symbol) as the biggest. So go with a.
