![](http://www.ecns.cn/hd/2022/04/06/a97d5a4509904589b3b95adbc59d772d.jpg)
Workers carry out the "tile-tapping' test" at the Sydney Opera House, April 5, 2022, Sydney, Australia. Every five years maintenance workers spend six weeks inspecting a tap test on each tile on the sails of the Sydney Opera House. (Photo/VCG)
![](http://www.ecns.cn/hd/2022/04/06/46d93e7bdca042c4919a8d7fa18032b0.jpg)
A worker carries out the "tile-tapping' test" at the Sydney Opera House, April 5, 2022, Sydney, Australia. Every five years maintenance workers spend six weeks inspecting a tap test on each tile on the sails of the Sydney Opera House. (Photo/VCG)
![](http://www.ecns.cn/hd/2022/04/06/d9c525eadaf446469a3548a553e6c6ea.jpg)
A worker carries out the "tile-tapping' test" at the Sydney Opera House, April 5, 2022, Sydney, Australia. Every five years maintenance workers spend six weeks inspecting a tap test on each tile on the sails of the Sydney Opera House. (Photo/VCG)
![](http://www.ecns.cn/hd/2022/04/06/c2da92887a1a4551a08d49ba702bf5b7.jpg)
A worker carries out the "tile-tapping' test" at the Sydney Opera House, April 5, 2022, Sydney, Australia. Every five years maintenance workers spend six weeks inspecting a tap test on each tile on the sails of the Sydney Opera House. (Photo/VCG)