Sentence Correction

During the 1980’s approximately $50 billion in private investment capital is estimated to have left Mexico and added to the strain on the country’s debt-ridden economy.

(A) During the 1980’s approximately $50 billion in private investment capital is estimated to have left Mexico and added
(B) During the 1980’s it is estimated that approximately $50 billion in private investment capital left Mexico and added
(C) It is estimated that there was approximately $50 billion in private investment capital that left Mexico during the 1980’s and added
(D) It is estimated that during the 1980’s approximately $50 billion in private investment capital left Mexico, adding
(E) Approximately $50 billion in private investment capital is estimated as having left Mexico during the 1980’s, adding

Source - 1000SC
OA - D....Please explain why others are eliminated

"and added" gives a feeling that the money was taken out from one place and added to another. But that's not what the sentence want to say.

The question says becoz of "$50 billion...... Mexico" the economy of Mexico got worse.

A, B, and C are out

Between D and E - D is rightly worded.

In this case "It" doesn't refer back to a noun. Is there a guideline for when it is ok to use "It" without that reference?