Though the task was difficult, they managed to complete it on time.

though 是连词，意思是"尽管、虽然"，用于引导让步状语从句，表示虽然存在某种情况，但主句的情况仍然成立。though 引导的从句可以放在句首或句末，放在句首时语气更正式一些。