问？？

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 fertilized 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) extended

(D) it extended

(E) is extending

答案是 a

and extending怎么能对呢？是省略了is 么？