With no explanation, label text_A→text_B with either "DON'T KNOW", "NO" or "YES".
text_A: The World Health Organization has classified radio frequency electromagnetic radiation as Group 2B - possibly carcinogenic. This group contains possible carcinogens such as lead, DDT, and styrene. By contrast, epidemiological studies looking for a relationship between cell phone use and brain cancer development, have shown that people who use cell phones more often actually exhibited less brain cancer than those who didn't own a phone, but were otherwise essentially identical in other regards, which thus demonstrates that any effect, even if it exists, cannot be large.
text_B: Does the passage still leave open the possibility that cell phones could be dangerous, but that the effect has been hidden by medical advances that have reduced brain-cancer from other causes?
NO.