Bài giải:

$\vartriangle ABC=\vartriangle MNO$do đó $\widehat{A}=\widehat{M};\widehat{B}=\widehat{N};\widehat{C}=\widehat{O}$

$\Rightarrow$$\widehat{M}=\widehat{A}={{55}^{0}}$ ; $\widehat{B}=\widehat{N}={{75}^{0}}$

Trong tam giác ABC có $\widehat{A}+\widehat{B}+\widehat{C}={{180}^{0}}$

$\Rightarrow \widehat{C}={{180}^{0}}-\widehat{B}-\widehat{A}$

$\Rightarrow \widehat{C}={{180}^{0}}-{{75}^{0}}-{{55}^{0}}={{50}^{0}}$

Đáp án đúng là B