Bài giải:

Theo bài ra ta có: $\widehat{B}=\widehat{A}+{{10}^{0}}$ , $\widehat{C}=\widehat{B}+{{10}^{0}}$ ; $\widehat{D}=\widehat{C}+{{10}^{0}}$

$\Rightarrow$ $\widehat{C}=\widehat{A}+{{10}^{0}}+{{10}^{0}}=\widehat{A}+{{20}^{0}}$

$\widehat{D}=\widehat{A}+{{20}^{0}}+{{10}^{0}}=\widehat{A}+{{30}^{0}}$

Xét tứ giác ABCD ta có:

$\widehat{A}$+ $\widehat{B}$+ $\widehat{C}$+ $\widehat{D}$ = 360⁰  (tổng các góc trong tứ giác)

Thay $\widehat{B}=\widehat{A}+{{10}^{0}}$ , $\widehat{C}=\widehat{A}+{{20}^{0}}$ ; $\widehat{D}=\widehat{A}+{{30}^{0}}$ ta có:

$\widehat{A}$+ $\widehat{A}+{{10}^{0}}+\widehat{A}+{{20}^{0}}+\widehat{A}+{{30}^{0}}$ = 360⁰

$\Rightarrow$4. $\widehat{A}$ = 300⁰

$\Rightarrow$$\widehat{A}$= 75⁰

$\widehat{B}=\widehat{A}+{{10}^{0}}$= 75⁰ + 10⁰ = 85⁰

$\widehat{C}=\widehat{A}+{{20}^{0}}$= 65⁰ + 20⁰ = 85⁰

$\widehat{D}=\widehat{A}+{{30}^{0}}$= 65⁰ + 30⁰ = 95⁰

Vậy đáp án đúng là: B