it was october 1,2009 that the prople's * ___its 60th birthday

问题描述:

it was october 1,2009 that the prople's * ___its 60th birthday
A.observed B.kept C.remined D.congratulated
并且说一下为什么

D庆祝
2009年10月1日,*庆祝建国60周年.