They failed to pass the exam last time, I regretted ______

A. life is not enjoyable since each age has some pains
B. young men can have the greatest happiness if they work hard
C. childhood is the most enjoyable time in one’s life
D. one is the happiest if he can make good use of each age in his life

A. can’t
B. won’t be able to
C. may not
D. shouldn’t