The alcohol shown is heated with concentrated acid. The secondary carbocation expands the four-membered ring to a more stable cation. Which structure is the major alkene?

The alcohol is 1-cyclobutylethanol. Ionisation gives a secondary cation next to a strained cyclobutane, and a ring-expansion alkyl shift gives the tertiary 1-methylcyclopentyl cation, relieving angle strain. Loss of a ring hydrogen then gives the Saytzeff product 1-methylcyclopentene, not the unrearranged vinylcyclobutane.