Which Unit Ratio Can Be Used to Change Feet to Inches

Multiple Choice

Which unit ratio can be used to change feet to inches?

A) $\frac { 1 \mathrm { ft } } { 12 \mathrm { in } . }$

B) $\frac { 1 \mathrm { mi } } { 5280 \mathrm { ft } }$

C) $\frac { 3 \mathrm { ft } } { 1 \mathrm { yd } }$

D) $\frac { 12 \mathrm { in } . } { 1 \mathrm { ft } }$