Step 1: Understand the concept of consumers.
- Primary consumers are herbivores, feeding on plants.
- Secondary consumers are carnivores, feeding on primary consumers.
Step 2: Identify the secondary consumer.
- The rat (A) and squirrel (B) are primary consumers because they eat plants.
- The grasshopper (D) is also a primary consumer (herbivore).
- The lizard (C) is a secondary consumer because it feeds on insects (primary consumers).
Final Answer:
\[
\boxed{(C) \; Lizard}
\]