CREATE TABLE table_6639 ("Series Ep." CLOB, "Episode" FLOAT, "Segment A" CLOB, "Segment B" CLOB, "Segment C" CLOB, "Segment D" CLOB)

What segment A is associated with a Segment D of manual motorcycle transmissions?
SELECT "Segment A" FROM table_6639 WHERE "Segment D" = 'manual motorcycle transmissions'
SELECT "Segment A" FROM "table_6639" WHERE "Segment D" = 'manual motorcycle transmissions'