SAT Improving Sentence Question?

<p>Mount St. Helens, a volcano that is undergoing a period of nearly
..............................................A.................... B.......... C
continuous eruption, annually grows at a rate of approximately 100 feet per year.
..................................................................................................... D
No Error.
........E</p>

<p>I think there's a redundancy issue with B or C?</p>

<p>(D), the answer, is redundant because "per year" does not need to be said after "annually." How are (B) and (C) possibly redundant?</p>

<p>Duh, stupid me. I don't know, it's under the redundancy questions, and I didn't think there was an issue with A or D, which would in essence, leave B & C.</p>