When was the start of the construction of the unit that's been in commercial operation since 04.03.1987?
CREATE TABLE table_17903 (
    "Unit" text,
    "Type" text,
    "Net power" text,
    "Total power" text,
    "Construction start" text,
    "Construction finish" text,
    "Commercial operation" text,
    "Shut down" text
)
SELECT "Construction start" FROM table_17903 WHERE "Commercial operation" = '04.03.1987'
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: When was the start of the construction of the unit that's been in commercial operation since 04.03.1987? ### Input: CREATE TABLE table_17903 (
    "Unit" text,
    "Type" text,
    "Net power" text,
    "Total power" text,
    "Construction start" text,
    "Construction finish" text,
    "Commercial operation" text,
    "Shut down" text
) ### Response: SELECT "Construction start" FROM table_17903 WHERE "Commercial operation" = '04.03.1987'