Sentence Correction

Centuries ago, biologists undertook the challenge of defining the term "species," however, even today, no single definition is universally accepted.

A. however, even today, no single definition is universally accepted.
B. but even today, have not universally accepted a single definition.
C. but even today, no single definition is universally accepted.
D. but today, no single definition is even universally accepted.
E. however, even today, a single definition is not universally accepted.

Source : Veritas Prep
Official Answer : C

Any idea how to delete duplicated post?