The right answer is E.
For the protection of American textile manufacturers against both Indian and Chinese competition, subsidies in 1994, introduced by Senate, which robbed US citizens the opportunity of buying inexpensive and high quality clothing.
A is not a complete sentence. There is no main clause. We have an opening modifier For the protection of American textile manufacturers against both Indian and Chinese competition followed by a noun subsidies, followed by a non-essential modifier introduced by Senate, and a relative clause. The subject subsidies does not have a verb.
B is incorrect because of parallelism error. Both is a parallelism marker and we expect X and Y to be parallel. X is against Indian, and Y is Chinese. X and Y are not parallel. To correct this error, against must precede both or Y must be against Chinese. We can eliminate B based on parallelism error.
In C, the non-underlined relative clause is intended to modify subsidies rather than Senate, since it is illogical to say that the Senate robbed the US citizens. In addition, subsidies are inanimate and therefore inacapable of having a purpose. For these same reasons, D can also be eliminated.
We are left with E as the best answer out of the lot. The relative clause rightly modifies subsidies.
A. For the protection of American textile manufacturers against both Indian and Chinese competition, subsidies in 1994, introduced by Senate, which robbed US citizens the opportunity of buying inexpensive and high quality clothing.
B. To protect American textile manufacturers both against Indian and Chinese competition, Senate introduced subsidies in 1994, which robbed US citizens the opportunity of buying inexpensive and high quality clothing.
C. In order to protect American textile manufacturers against both Indian and Chinese competition, subsidies were introduced by the Senate in 1994, which robbed US citizens the opportunity of buying inexpensive and high quality clothing.
D. In order to protect American textile manufacturers against Indian, as well as against Chinese, competition, subsidies in 1994 were introduced by the Senate, which robbed US citizens the opportunity of buying inexpensive and high quality clothing.
E. For protecting American textile manufacturers against Indian, as well as Chinese, competition, Senate introduced subsidies in 1994, which robbed US citizens the opportunity of buying inexpensive and high quality clothing.