A、A cure to brain cancer. B、A new surgical instrument. C、A pen that can identify cancerous tissue. D、A new drug that can elimina

A handheld device can identify cancerous tissue in 10 seconds, according to scientists at the University of Texas. They say it could make surgery to remove a tumour quicker, safer and more precise. Tests suggest the technology is accurate 96% of the time. The MasSpec Pen takes advantage of the unique metabolism of cancer cells. Their furious drive to grow and spread means their internal chemistry is very different to that of healthy tissue. The challenge for surgeons is finding the border between the cancer and normal tissue. In some tumours it is obvious, but in others the boundary between healthy and diseased tissue can be blurred. The pen should help doctors ensure none of the cancer is left behind. Remove too little tissue, and any remaining cancerous cells will grow into another tumour. But take too much, and you can cause damage, particularly in organs such as the brain. Livia Eberlin, an assistant professor of chemistry at the University of Texas, Austin, said: "What’s exciting about this technology is how clearly it meets a clinical need. The tool is elegant and simple and can be in the hands of surgeons in a short time."
Questions 3 and 4 are based on the news report you have just heard.
3. What is this news report mainly about?
4. What challenge do surgeons face?