Sentence Correction

Please help to solve this SC problem

The single-family house constructed by the Yana, a Native American people who lived in what is now Northern California, was conical in shape, its framework of poles overlaid with slabs of bark, either cedar or pine, and banked with dirt to a height of three to four feet.

a. banked with dirt to a height of
b. banked with dirt as high as that of
c. banked them with dirt to a height of
d. was banked with dirt as high as
e. was banked with dirt as high as that of

This is primarily an issue of parallel construction. poles overlaid with x... and banked with y
Eliminate c,d and e. (Note c has a problematic "them" as well.) In B, the phrase "as high as that of" is strange. What is "that?"
Only A maintains parallel construction without introducing another error.