These are not the only acceptable answers, or even the best answers. These are just examples of good answers.
Gravity is also only attractive.
The electrical force only acts between objects that have charge, and can be attractive or repulsive. The electrical force is much stronger than gravity. The last part is somewhat arguable, since comparing Coulombs and kilograms is like comparing apples and oranges. However, there are two observations that support the electrical force being stronger than gravity. In the force equations, the proportionality constant for electrical force is much, much larger than the proportionality constant for the gravitational force.