X, Y and Z are three hydrocarbons made up only of carbon and hydrogen. X: $\text{CH}_2=\text{CH}_2$ Y: $\text{CH}_3-\text{CH}=\text{CH}_2$ Z: $\text{CH}_3-\text{CH}_2-\text{CH}=\text{CH}_2$ What feature is shared by compounds X, Y and Z?
- A1, 2 and 3
- B1 and 2 only
- C1 and 3 only
- D2 and 3 only