(A) Home buyers should double-check their mortgage payment calculation, as the British program Watchdog reported that two-thirds of all borrowers are overpaying because of errors in interest payment calculations.
correct answer home..... calculation (independent clause),as.....(dependent clause). The sentence is structured concisely.
(B) Home buyers should double-check their mortgage payment calculation, as the British program Watchdog reported that all borrowers are overpaying two-thirds because of errors in interest payment calculations.
distorted meaning- overpaying two thirds
(C) Because of errors in interest rate payment calculations, home buyers should double-check their mortgage payment calculation, as two-thirds of all borrowers are overpaying, according to a report by the British program which is known as Watchdog.
illogical constructio[b] there can't be 2 dependent clauses
(D) Home buyers should double-check their mortgage payment calculation, since as to the British program Watchdog reported that two-thirds of all borrowers are overpaying because of errors in interest payment calculations.
[b]redundant- since as(any one is enough)
(E) Home buyers should double-check their mortgage payment calculation, according to the British program Watchdog, reported that two-thirds of all borrowers are overpaying because of errors in interest payment calculations.
[/b]illogical construction[/b]-reported connects calculation