关于不定代词a的一种用法1.I don't think it possible to finish ____ proje

关于不定代词a的一种用法
1.I don't think it possible to finish ____ project as difficult as this within____ given little time.
A./;a B.a;the C.the;/ D.the;a
2.------You shouldn't have made ____ promise that you can never keep.
------- But I didn't want to lose _____ chance.
A.a;the B.the;a C.a;a D.a;/
这两题里面的第一空都是选择的不定冠词a 但是我没办法解释 后面不是都还有修饰成分么 按理说应该选用the啊