Since the 1970s, in the face of a swoman vere loss of market share in dozens of industries, manufacturers in the United states .... to improve productivity and

Since the 1970s, in the face of a swoman vere loss of market share in dozens of industries, manufacturers in the United states .... to improve productivity and therefore enhance their international competitiveness-through cost-cutting programs.
(A) have been trying
(B) has been trying
(C) had been trying
(D) was trying
(E) is trying