What significance does October 1 1949 have in Chinese history?

Question

a. The Boxer Rebellion was defeated by foreign troops
b. The last dynasty ended with the death of its empress
c. Mao Zedong declared China "The People's Republic of China"***
d. China ended its self-imposed isolation

Just checking my work:)
*** - My Answer

Thanks,
Kaai97

Answer 1

Correct.

Answer 2

my answer don't look like this