there are certainly times when giving up trying is the right thing to do in most cases a

问题补充：

there are certainly times when giving up trying is the right thing to do, in most cases all needed is commitment and communication.

A. Unless

B. Before

C. Although

D. Since

答案：

A. Unless

B. Before

(答案→)C. Although

D. Since

解析：句意：虽然有一定的时候放弃尝试是正确的事情,在大多数情况下都需要的是承诺和沟通。这两句话是转折关系，用although“虽然”，A. Unless除非，如果不，B. Before在…前面， D. Since自从，所以选C。