In the food chain below, which is the producer?

flower - mouse - snake - hawk

The question is asking us the following: "In the food chain below, which is the producer? And the food chain is: flower - mouse - snake - hawk", The producer is the organism that can produce energy from the source, typically from the sunlight, without eating parts of other animals. Producers are plants - and almost all plants are produces (some are also consumers). so the answer is "flower'