William Hornby acquired bison herds for breeding stock hoping that this move would eventually lead to increasing in their numbers, and a fortification of their environment.
A. increasing in their numbers,
B. an increase in their numbers,
C. their increase in numbers,
D. an increasing in numbers,
E. an increasing in the numbers of them,
D for parallelism ...E is incorrect coz "the numbers" should be "the number"
Editted: oops, I meant B ...hik, what's wrong with me, I thought of sth and picked sth else