Find the Dimensions of the Matrix $B = \left[ \begin{array} { c } \frac { 2 } { 3 } \\3 \\0 \\- \frac { 4 } { 7 }\end{array} \right]$

Multiple Choice

Find the dimensions of the matrix $B = \left[ \begin{array} { c } \frac { 2 } { 3 } \\3 \\0 \\- \frac { 4 } { 7 }\end{array} \right]$
And identify the value of the element $b _ { 21 }$ .

A) $1 \times 4$ ; $b _ { 21 } = 3$
B) $4 \times 1$ ; $b _ { 21 } = 3$
C) $1 \times 4$ ; $b _ { 21 } = - \frac { 4 } { 7 }$
D) $4 \times 1$ ; $b _ { 21 } = 0$
E) $1 \times 4$ ; $b _ { 21 } = \frac { 2 } { 3 }$