Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
What is the main use for the structure listed in walker city, iowa?

### Inputs:
table_name: table, columns: ['Pinnacle height', 'Year', 'Structure type', 'Main use', 'Country', 'Town']

### Response:
SELECT Main use FROM table WHERE Town = walker city, iowa