This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.
Q: On 21 April, Communist forces crossed the Yangtze River. On April 23, 1949, the Communist People's Liberation Army (PLA) captured Nanjing. The KMT government retreated to Canton (Guangzhou) until October 15, Chongqing until November 25, and then Chengdu before retreating to Taiwan on December 10. By late 1949, the PLA was pursuing remnants of KMT forces southwards in southern China, and only Tibet was left. After the establishment of the People's Republic of China in October 1949, Nanjing was initially a province-level municipality, but it was soon merged into Jiangsu province and again became the provincial capital by replacing Zhenjiang which was transferred in 1928, and retains that status to this day.
A:
When did the Communist troops cross the Yangtze River?