Because the number of surgeons is growing faster than the number of operations and because noninvasive medical therapies are increasingly replacing surgery, the average annual number of operations per surgeon has fallen by one-fourth in recent years. It can be concluded that, if these trends continue, a dangerous decline in the level of surgical skill will occur.
The argument above is based on which of the following assumptions?
(A) A surgeon's skill cannot be properly maintained unless the surgeon performs operations with a certain minimum frequency.
(B) Surgeons now spend a large percentage of their time performing noninvasive medical procedures.
(C) All doctors, but especially surgeons, are receiving poorer training in medical school than they were a few years ago.
(D) The level of skill of each individual surgeon has declined in recent years.
(E) Some experienced surgeons are now performing a greater number of operations than they used to perform.