There were extraordinary security measures at the compound, including 3-5 metre-high walls topped with barbed wire.
另外这个院子有特别的安全措施，3至5米高的院墙上还装有铁丝网。
2
The metal particles, which were five nanometres (billionths of a metre) across, were themselves coated with a photosensitive compound called azobenzene.