External environmental causes of cancer are factors in the environment that increase risk of cancer such as air pollution, UV radiation and indoor radon.
外部环境致癌因素是指环境中导致罹患癌症的危险升高的因素，如空气污染、紫外线辐射及室内的氡等。
2
They do not protect against externalradiation, or against any other radioactive substances besides radioactive iodine.
他们不能阻止外部的辐射、或是任何其他辐射形式。
3
These are the bunkers for temporary shelter in case of contingency. One can be here for some days, controlling radiation situation in the station and keeping connection with external world.