Let's work on the first pair of compounds. Are they the same compound? They aren't. They have different formulas (the one that is above has two more H atoms) so they are unrelated.
a) Unrelated
These compounds have the same formula, but they are not the same compound. In the first one the O is bonded to the second C, and in the other compound is bonded to the third C. They have the same formula but different configuration, so they are structural isomers.
b) Structural isomers.
They both have 6 C atoms and 14 H atoms. They have the same formula but different structure. So they are structural isomers.
c) Structural isomers.
They both have 4 atoms of C and 10 atoms of H. As the previous pair of compounds, they have the same formula but different structure. They are structural isomers.
d) Structural isomers.
They both have 4 atoms of C, 1 atom of O and 8 atoms of H. They have the same formula, but, do they have different structure? No they don't. The O is bonded to the C number 2 in both compounds. They are the exactly same compound.
e) Same