My range - which exercises

My current range is D3-C5. As a 70 yearold female should I practice tenor or alto exercises?

Hi, Carolyn! You may be comfortable using either. Tenor range exercises typically won't go far below C3 or above C5, and alto range exercises typically won't go far below E3 or above E5. Since you fall between the two, I recommend trying both and using whichever feels like a more comfortable fit. You can switch it up depending on the day as well (feeling especially low, use tenor, feeling a bit lighter or up for a stretch, use alto).