In the poem “My Last Duchess,” what does the duke mean when he says that “This grew; I gave commands; / Then all smiles stopped together？”

In the poem “My Last Duchess,” what does the duke mean when he says that “This grew; I gave commands; / Then all smiles stopped together？”
A.He ordered the duchess to keep silence.
B.He required the duchess to be solemn.
C.He murdered the duchess.
D.He locked up the duchess.
正确答案：He murdered the duchess.