The correct answer is False. Planning graphs can be used to solve a variety of planning problems, including those that are not prepositional.
A planning graph is a data structure that is used to represent the state of a planning problem and the possible actions that can be taken to achieve a goal state. Planning graphs are typically used to solve problems in which the state of the world can be represented as a set of propositional atoms. However, they can also be used to solve problems in which the state of the world is more complex, such as problems that involve continuous variables or actions that have multiple effects.
One advantage of planning graphs is that they can be used to efficiently solve problems that are large or complex. Another advantage is that they can be used to generate plans that are guaranteed to be optimal. However, planning graphs can also be difficult to construct and use, especially for problems that are large or complex.
In conclusion, planning graphs are a powerful tool for solving planning problems. However, they are not limited to prepositional planning problems.