Photo taken on April 19, 2019 shows a view of the Royal Greenhouses of Laeken in Brussels, Belgium. Every spring, the Royal Greenhouses of Laeken are open to the public for 3 weeks. This year the greenhouses are available for the public from April 19 to May 10. (Xinhua/Zheng Huansong)

A tourist visits the Royal Greenhouses of Laeken in Brussels, Belgium, April 19, 2019. Every spring, the Royal Greenhouses of Laeken are open to the public for 3 weeks. This year the greenhouses are available for the public from April 19 to May 10. (Xinhua/Zheng Huansong)

Tourists visit the Royal Greenhouses of Laeken in Brussels, Belgium, April 19, 2019. Every spring, the Royal Greenhouses of Laeken are open to the public for 3 weeks. This year the greenhouses are available for the public from April 19 to May 10. (Xinhua/Zheng Huansong)

Tourists visit the Royal Greenhouses of Laeken in Brussels, Belgium, April 19, 2019. Every spring, the Royal Greenhouses of Laeken are open to the public for 3 weeks. This year the greenhouses are available for the public from April 19 to May 10. (Xinhua/Zheng Huansong)

A tourist visits the Royal Greenhouses of Laeken in Brussels, Belgium, April 19, 2019. Every spring, the Royal Greenhouses of Laeken are open to the public for 3 weeks. This year the greenhouses are available for the public from April 19 to May 10. (Xinhua/Zheng Huansong)

A tourist visits the Royal Greenhouses of Laeken in Brussels, Belgium, April 19, 2019. Every spring, the Royal Greenhouses of Laeken are open to the public for 3 weeks. This year the greenhouses are available for the public from April 19 to May 10. (Xinhua/Zheng Huansong)

Tourists visit the Royal Greenhouses of Laeken in Brussels, Belgium, April 19, 2019. Every spring, the Royal Greenhouses of Laeken are open to the public for 3 weeks. This year the greenhouses are available for the public from April 19 to May 10. (Xinhua/Zheng Huansong)

Photo taken on April 19, 2019 shows a view of the Royal Greenhouses of Laeken in Brussels, Belgium. Every spring, the Royal Greenhouses of Laeken are open to the public for 3 weeks. This year the greenhouses are available for the public from April 19 to May 10. (Xinhua/Zheng Huansong)

Tourists visit the Royal Greenhouses of Laeken in Brussels, Belgium, April 19, 2019. Every spring, the Royal Greenhouses of Laeken are open to the public for 3 weeks. This year the greenhouses are available for the public from April 19 to May 10. (Xinhua/Zheng Huansong)

Tourists visit the Royal Greenhouses of Laeken in Brussels, Belgium, April 19, 2019. Every spring, the Royal Greenhouses of Laeken are open to the public for 3 weeks. This year the greenhouses are available for the public from April 19 to May 10. (Xinhua/Zheng Huansong)

Photo taken on April 19, 2019 shows a view of the Royal Greenhouses of Laeken in Brussels, Belgium. Every spring, the Royal Greenhouses of Laeken are open to the public for 3 weeks. This year the greenhouses are available for the public from April 19 to May 10. (Xinhua/Zheng Huansong)

Photo taken on April 19, 2019 shows a view of the Royal Greenhouses of Laeken in Brussels, Belgium. Every spring, the Royal Greenhouses of Laeken are open to the public for 3 weeks. This year the greenhouses are available for the public from April 19 to May 10. (Xinhua/Zheng Huansong)

Tourists visit the Royal Greenhouses of Laeken in Brussels, Belgium, April 19, 2019. Every spring, the Royal Greenhouses of Laeken are open to the public for 3 weeks. This year the greenhouses are available for the public from April 19 to May 10. (Xinhua/Zheng Huansong)

Photo taken on April 19, 2019 shows a view of the Royal Greenhouses of Laeken in Brussels, Belgium. Every spring, the Royal Greenhouses of Laeken are open to the public for 3 weeks. This year the greenhouses are available for the public from April 19 to May 10. (Xinhua/Zheng Huansong)