**Explanation:**

The boiling point of a compound is determined by the strength of the intermolecular forces between its molecules. In the case of cis and trans isomers, the arrangement of atoms around the double bond affects the intermolecular forces and therefore the boiling point.

**Cis Isomer:**
The cis isomer has the same functional groups on the same side of the double bond. This results in a bent or "U" shape in the molecule. The bent shape allows for closer proximity between molecules, leading to stronger intermolecular forces.

**Trans Isomer:**
The trans isomer has the same functional groups on opposite sides of the double bond. This results in a linear or "Z" shape in the molecule. The linear shape allows for less close proximity between molecules, leading to weaker intermolecular forces.

**Effect on Boiling Point:**
Stronger intermolecular forces require more energy to break, resulting in a higher boiling point. Therefore, the cis isomer, with its stronger intermolecular forces, will have a higher boiling point compared to the trans isomer.

This can be further explained by considering the types of intermolecular forces present. In the case of cis isomers, the bent shape allows for the formation of dipole-dipole interactions between polar functional groups. These dipole-dipole interactions are stronger than the London dispersion forces present in trans isomers.

Overall, cis isomers have a higher boiling point than trans isomers due to the stronger dipole-dipole interactions resulting from their bent molecular shape. Therefore, option 'A' is the correct answer.