Addition Reactions in Organic Chemistry

In organic chemistry, addition reactions involve the addition of atoms or groups to a double or triple bond in an organic compound. A common example is the reaction of an alkene with a hydrogen halide, such as HCl. In this process, the double bond opens up, allowing the hydrogen and halide to add across the former double bond. Which of the following compounds is most likely to undergo an addition reaction when reacted with hydrochloric acid?