Can you please go over this question? From Practice SAT 2005, Section 5, Question #27: “Paul Ecke, flower grower and hybridizer, A. became B. known as “Mr. Poinsettia” after developing new varieties of the flower and C. by pioneering it D. as a living symbol of Christmas. E. No Error

I chose C (by pioneering) because I thought the “by” was a bit unnecessary to use (and I guess, unparallel as well).

You’re correct. He became known as “Mr. Poinsettia” after doing 2 things:

1. developing new varieties of the flower and
2. pioneering it as a living symbol of Christmas.

The “by” has no place in that structure.