I have been exercising regularly, and I __________ stronger and healthier.
A) am feeling B) feel C) will feel D) had felt
Hello, Izzat Hannah—Like Gustavo, I think that "am feeling" is the best choice, a normal context being assumed. The present progressive conveys the right meaning, of a process or development that is unfolding.
The present perfect progressive ("have been exercising regularly") leads the listener to assume that the regular exercise is ongoing even at the present time, and that the bodily development it has led to may be expected to continue.
But perhaps the speaker is an astronaut who has been getting ready for space flight. He may wish to say simply that he feels stronger and healthier now (pre-launch) as a result of the regular exercise he has been getting. 