Which of the following is a complex rocket?

A complex rocket encompasses both the configurations of clustered rocket motors and multi-stage rockets.

Clustered rocket motors refer to scenarios where multiple engines are used together to create more thrust than a single motor could provide. This setup can be essential for larger rockets that require significant lift-off power. The intricacies involved in the design, deployment, and control of multiple engines contribute to the classification of these rockets as complex.

On the other hand, a rocket with more than one stage involves a sequential firing of stages that discard parts of the rocket as fuel is burned, enabling it to reach higher altitudes and velocities. This stage separation is a sophisticated approach that optimizes the rocket's performance and is characteristic of more advanced rocket designs.

While the design for international competitions may involve complexities, simply being designed for competition does not inherently render a rocket complex. The key features that define a complex rocket are its use of clustered motors and multi-stage configurations, making option B a comprehensive choice that accurately encompasses both definitions.