Which structures represent 2-methylbutane? check all that apply?

2-methyl butane is an organic compound with a molecular formula of C5H12,
Isomers are compound with the same molecular formula but different structural formula. Therefore 2-methyl butane may exhibit isomerism and may be represented in different structural formulas but maintaining the same molecular formula. I believe that the structures that represent 2-methyl butane will be
a, b,c, and d.

Where is the picture at