Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_2911781_3 (constructor VARCHAR, grand_prix VARCHAR)
### Question:
What was the constructor in the Belgian Grand Prix round?
### Answer:
SELECT constructor FROM table_2911781_3 WHERE grand_prix = "Belgian grand_prix"