Which of the following does the author cite in support of the quotation from the United Nations Scientific Committee on the Effects of Atomic Radiation？( )Ⅰ.Strontium 90 and carbon 14 become incorporated into the body and deliver radiation for an entire lifetime.Ⅱ.An abnormally high percentage of patients with arthritis of the spine who were treated with X rays contracted cancer.Ⅲ.A high incidence of cancer appeared among children of mothers who had been given prenatal pelvic X rays.

A.Ⅰ only.
B.Ⅰ，Ⅱ，and Ⅲ.
C.Ⅰ and Ⅱ only.
D.Ⅱand Ⅲ only.