According to the international investment memorandum recently signed in Geneva, France is one of the 4 European nations
planning to provide fewer tax incentives for foreign investment in production of heavy industrial machinery.
(A) planning to provide fewer -> fewer is used for countable nouns and it can be in plural. It makes sense to "one of the 4 European nations". Let's keep it.
(B) planning to provide less -> Less can't be used as plural. Incorrect.
(C) planning on providing fewer -> Providing is incorrect.
(D) which is planning on providing fewer -> Same error repeated. Incorrect.
(E) that is planning to provide less -> Same as B.
So, I think A.