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

### Instruction:
Tell me the average gross tonnage for april 1919 entered service

### Inputs:
table_name: table, columns: ["Ship's name", 'Entered service', 'Ended service', 'Gross Tonnage', 'Type of Vessel']

### Response:
SELECT AVG Gross Tonnage FROM table WHERE Entered service = april 1919