The correct answer is $\boxed{\text{B}}$.
Pantene is a hydrocarbon with the molecular formula $C_{10}H_{20}$. It is a straight-chain alkane with 10 carbon atoms. The structural formula of pentene is shown below:
$$\ce{CH3-CH2-CH2-CH2-CH=CH2}$$
Butene is a hydrocarbon with the molecular formula $C_4H_8$. It is an alkene with 4 carbon atoms and one double bond. The structural formula of butene is shown below:
$$\ce{CH3-CH2-CH=CH2}$$
Ethene is a hydrocarbon with the molecular formula $C_2H_4$. It is an alkene with 2 carbon atoms and one double bond. The structural formula of ethene is shown below:
$$\ce{CH2=CH2}$$
Propene is a hydrocarbon with the molecular formula $C_3H_6$. It is an alkene with 3 carbon atoms and one double bond. The structural formula of propene is shown below:
$$\ce{CH3-CH=CH2}$$
Therefore, the only option that matches the structural formula of pentene is $\boxed{\text{B}}$.