Efe made six shots in a basketball practice. After each shot, Efe noted what fraction of his shots up to that point had been successful. The largest of these six numbers that Efe noted is $\frac{3}{4}$.
If exactly four of Efe's shots were successful, which shots were not successful?
A) 1st and 4th
B) 1st and 5th
C) 1st and 6th
D) 2nd and 5th
E) 2nd and 6th