aCho hình chóp S.ABCD có đáy ABCD là một hình bình hành. Gọi A', B', C' lần lượt là

Ta có: $\left\{\begin{array}{l}{\mathrm{B}}^{\text{'}}{\mathrm{C}}^{\text{'}}\text{\hspace{0.17em}//\hspace{0.17em}}\mathrm{AD}\\ {\mathrm{B}}^{\text{'}}{\mathrm{C}}^{\text{'}}\not\subset \left(\mathrm{ACD}\right)\end{array}\right.\Rightarrow {\mathrm{B}}^{\text{'}}{\mathrm{C}}^{\text{'}}\text{\hspace{0.17em}//\hspace{0.17em}}\left(\mathrm{ACD}\right)\left(1\right)$

$\left\{\begin{array}{l}{\mathrm{A}}^{\text{'}}{\mathrm{B}}^{\text{'}}\text{\hspace{0.17em}//\hspace{0.17em}}\mathrm{CD}\\ {\mathrm{A}}^{\text{'}}{\mathrm{B}}^{\text{'}}\not\subset \left(\mathrm{ACD}\right)\end{array}\right.\Rightarrow {\mathrm{A}}^{\text{'}}{\mathrm{B}}^{\text{'}}\text{\hspace{0.17em}//\hspace{0.17em}}\left(\mathrm{ACD}\right)\left(2\right)$

Từ (1), (2) $\Rightarrow \left({\mathrm{A}}^{\text{'}}{\mathrm{B}}^{\text{'}}{\mathrm{C}}^{\text{'}}\right)\text{\hspace{0.17em}//\hspace{0.17em}}\left(\mathrm{ACD}\right).$

+ Đáp án A sai vì ${\mathrm{A}}^{\text{'}}{\mathrm{B}}^{\text{'}}\subset \left(\mathrm{SAB}\right)$.

+ Đáp án C sai vì ${\mathrm{A}}^{\text{'}}{\mathrm{B}}^{\text{'}}\cap \mathrm{SB}=\left\{{\mathrm{B}}^{\text{'}}\right\}$.

+ Đáp án D sai vì ${\mathrm{B}}^{\text{'}}\mathrm{C}\cap {\mathrm{BC}}^{\text{'}}$.

Chọn đáp án B.