Tatsouka 2009

What is the value of $7$ $\dfrac{4}{6}$ $-$ $3$ $\dfrac{5}{6}$?
A. $3\dfrac{5}{6}$
B. $\dfrac{3}{4}$
C. $\dfrac{5}{4}$
D. $1$
E. $\dfrac{5}{2}$