Question

_______ it got dark,they worked hard there.

 A. Though                                                                    B. If

 C. Since                                                                       D. Because

Answer 1

A  though“尽管”；if“如果，是否”；since“因为；自从”；because“因为”。根据句意“尽管天黑了，他们仍在那里努力工作”可知选A。