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The correct answer is $\boxed{\text{C}}$.
Butane has the molecular formula $C_4H_{10}$. It has two structural isomers, which are different compounds with the same molecular formula but different arrangements of the atoms. The two structural isomers of butane are n-butane and isobutane.
- n-Butane is the straight-chain isomer of butane. It has the following structural formula:
$$H_3C-CH_2-CH_2-CH_3$$
- Isobutane is the branched-chain isomer of butane. It has the following structural formula:
$$H_3C-CH(CH_3)-CH_3$$
The two isomers of butane have different physical properties. n-Butane is a gas at room temperature, while isobutane is a liquid. n-Butane has a higher boiling point than isobutane.