<p>Zizi, most bio-related majors take the 17 series. It’s in the title- Calculus for Biologists…</p>
<p>Anywho, the 21 series is probably the most difficult of the series because the teachers grade more rigorously and expect more out of you. That being said, it won’t really get too hard until 21C but even though if you come to class, do your homework, and prepare well you can very well get an A. I slacked off in 21B and 21C, never went to class, studied the day before midterms and finals and still pulled off B’s. </p>
<p>But for your major I would recommend taking the 17 series because you learn a little bit of biology too. 16 is fine too but you don’t get as much credit for it. One of my friends who took 16, he was very intelligent, I might add, told me he took it instead of 17 or 21 because he wanted to do better, and that the 17 series is overrated.</p>
<p>My 2 cents.</p>