Machines replacing human labor, there was wide anticipation that the

As it looks to me, this is more of a problem of conjugating a modifier with its modified noun. The participial modifier- replacing - or - being replaced - are simply dangling without a connection to what it can modify. Immediately after the modifier phrase, what it ever it intends to modify must be present.

A. Machines replacing human labor, there was wide anticipation that

E. Human labor being replaced by machines, there was wide anticipation that

For this reason, we can reject A and E.

The next best thing will be to conjugate the two independent things by a sub-coordinating conjunction obviating the need for the modified noun to appear after the introductory clause.

Now analyzing each the choices of B, C and D,

B. When machines replaced human labor, there was wide anticipation ---- When denotes a happening at a particular point, while the text is more about generalization; meaning gets distorted and narrowed down

C. As machines replaced human labor, it was widely anticipated that ---- The best among the lot; As denotes a general happening and also denotes sort of an on-going tinge.

D. Insofar as machines replaced human labor, it was widely anticipated – - insofar as - means up to the point; as long as -; this conjunction also limits the scope of the intended generalization

C eventually