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

### Instruction:
What is the name of a partner that played on a hard surface on 18 April 2011?

### Inputs:
table_name: table, columns: ['Date', 'Tournament', 'Surface', 'Partner', 'Opponent in the final', 'Score']

### Response:
SELECT Partner FROM table WHERE Surface = hard AND Date = 18 april 2011