Question

【题目】 , you should do it well(now)
既然你已决定做这件事，就应该把它做好。

Answer 1

【答案】Now that you have decided to do it
【解析】now that固定短语，“既然”。根据句意，谓语动词用现在完成时，因此答案为Now that you have decided to do it。