单项选择题A.It involved 13, 000 researchers from Asia, Europe and America.B.It was conducted in seven Mid-Eastern countries in the 1950s.C.It is regarded as one of the greatest researches of its kind.D.It has drawn the attention of medical doctors the world over.
A.It
B.
B.It
C.
C.It
D.
D.It
E.