The benefits of the new policies are far reaching, economic experts

The benefits of the new policies are far reaching, economic experts say, providing a powerful vehicle to chip away at poverty in other countries and expanding the earnings of immigrants in the United States.

A)far reaching, economic experts say, providing a powerful vehicle to chip away at poverty in other countries and expanding the earnings of immigrants in the United States.
Correct. "providing" and "expanding" modify "the benefits" correctly.

B)far reaching, economic experts say, as it is providing a powerful vehicle to chip away at poverty in other countries and expand the earnings of immigrants in the United States.
Wrong. "The benefits" is plural. Bad grammar structure.

C)far reaching, economic experts say, providing a powerful vehicle to chip away at poverty and expand the immigrants’ earnings in the United States.
Wrong. Not parallel.

D)far reaching, economic experts say, by providing a powerful vehicle to chip away at poverty in other countries while it expands the earnings of immigrants in the United States.
Wrong. Parallelism problem + "The benefits" is plural.

E)far reaching, economic experts say, in that they provide a powerful vehicle to chip away at poverty in other countries expanding the earnings of immigrants in the United States.[/quote]
Wrong. "They" refers to the benefits or experts? + Parallelism problem.

Hope it helps.