Direct ecosystem services refer to the tangible benefits that people receive directly from ecosystems. Among the options listed, "recreational parks" is the most fitting choice as a direct ecosystem service because it provides recreational opportunities and benefits to people directly from the ecosystem.
The other options relate to processes (photosynthesis and soil decomposition) that support ecosystem function but are not direct benefits to humans in the same way that recreational parks are. "Transportation" is generally not considered an ecosystem service in this context.
So, the best answer is recreational parks.