Useful protein drags, such as insulin, mus

题目：

Useful protein drags, such as insulin, must still be administered by the cumbersome procedure of injection under the skin. If proteins are taken orally, they are digested and cannot reach their target cells. Certain nonprotein drags, however, contain chemical bonds that are not broken clown by the digestive system. They can, thus, be taken orally.
The statements above most ply support a claim that a research procedure that successfully accomplishes which of the following would be beneficial to users of protein drugs

A．Coating insulin with compounds that are broken down by target cells, but whose chemical bonds are resistant to digestion.

B．Converting into protein compounds, by procedures that work in the laboratory, the nonprotein drugs that resist digestion.

C．Removing permanently from the digestive system any substances that digest proteins.

D．Determining, in a systematic way, what enzymes and bacteria are present in the normal digestive system and whether they tend to be broken down within the body.

E．(E) Determining the amount of time each nonprotein drug takes to reach its target cells.