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_12983929_1 (construction_start VARCHAR, net_power VARCHAR, unit VARCHAR)
### Question:
When did the construction of the unit Chinon B1 with net power of 905 MW start?
### Answer:
SELECT construction_start FROM table_12983929_1 WHERE net_power = "905 MW" AND unit = "Chinon B1"