Why can't I sing low notes? Is there any exercise that can help me?

While it is natural for you to be able to sing the higher notes since you are a tenor, there are exercises that you can do to help widen your range. If you sing on a syllable such as "ha," "Hee," etc., start on a higher note and work your way down by singing scales or arpeggios,This will help lower your vocal range. You can also start at a high pitch and slide down as far as your voice will go. Try this a few times. You should start small and gradually go lower everyday. As you sing lower, go back up a few steps, then go down again, even further. This will stretch your range and condition vocal chords. Your vocal chords are like other muscles, you can exercise them and work them out to make them more flexible. But doing too much at once can damage them, so take it step by step.