A. had been below 5%, the board of directors would have recommended that all further investments must
would have recommended that all further investments must, this is not idiomatic, it should be recomended that be kept, Wrong answer
B. was below 5%, the board of directors would have recommended that all further investments should
the construction is not correct, If+simple past + conditional ( usually Would...) Wrong answer
C. was below 5%, the board of directors would recommend that all further investments
in cond type two where the sentence refers to hypothetical or unlikely situation in the present or future, always it should be "were" rather than was, indepandently of the pronoun, Wrong answer
then it's the correct answer[/u]
D. were below 5%, the board of directors would recommend that all further investments
This sentences refers to hypothetical or unlikely situation in the present plus [u]This is the correct answer, This sentence refers to hypothetical situation in the past and Here, the “if clause” uses the past tense and the main clause uses the conditional perfect tense with ' would " ,plus the end of the sentence ( recommand that X be Y) is idiomatic
E. would have been below 5%, the board of directors would have recommended that all further investments would
would have recommended that all further investments would, this is not idiomatic, it should be recomended that be kept, Wrong answer