Its straightforward E

patent laws -> increased investment in dev of new products -> increase in manufacturer's productivity

Now
(A) Stronger patent laws tend to benefit financial institutions as well as manufacturers. (Fin insti aren't discussed)
(B) Increased productivity in manufacturing is likely to be accompanied by the creation of more manufacturing jobs. (jobs aren't discussed)
(C) Manufacturers will decrease investment in the development of new products and technologies unless there are stronger patent laws. (premises don't consider opposite scenario i.e. missing patent laws)
(D) The weakness of current patent laws has been a cause of economic recession. (economic recession where does this come in picture now)
(E) Stronger patent laws would stimulate improvements in productivity for many manufacturers.

(A) Stronger patent laws tend to benefit financial institutions as well as manufacturers. [ financial institutions are not discussed in the passage. out of scope]

(B) Increased productivity in manufacturing is likely to be accompanied by the creation of more manufacturing jobs. [ out of scope again!]

(C) Manufacturers will decrease investment in the development of new products and technologies unless there are stronger patent laws. [This is exact reverse of the stimulus. the passage tells us stronger patents ->manufacturers would be encouraged to invest. but this choice tells us that manufacturers will not decrease investment -> stronger patent laws.
The sufficient condition in the stimulus is converted into a necessary condition in the answer choice. Eliminated!]

(D) The weakness of current patent laws has been a cause of economic recession. [ again out of scope!]

(E) Stronger patent laws would stimulate improvements in productivity for many manufacturers. [correct. this is directly reqorded from the stimulus]

Hope this helps!