OG SC 210、どなたか分かりますか？

210. Scientists have recently discovered what could be the largest and oldest living organism on Earth, a giant fungus that is an interwoven filigree of mushrooms and rootlike tentacles spawned by a single fertilizer spore some 10,000 years ago and <extending> for more than 30 acres in the soil of a Michigan forest.
A) extending
B) extends
C)it extended
D)it extended
E)is extending

正解はAで分かるんですが、Eの駄目な理由が分かりません。どなたか教えてもらえますか。

http://tools.geocities.co.jp/CollegeLife-Cafe/6302/@geoboard/