The arrival of which ally in 1917 was a turning point in the war because, it stopped the stalemate on the western front?

It was the arrival of the United States in 1917 that was a turning point in the war because, it stopped the stalemate on the Western Front, since the US brought with it great industrial power. 

Sir thomas more, venerated in the catholic church as saint thomas more, was an english lawyer, social philosopher, author, statesman, and noted renaissance humanist. he was also a councillor to henry viii, and lord high chancellor of england from october 1529 to 16 may 1532. i found this information on wikipedia

Your answer is d)magnesium