![](https://cos-cdn.shuashuati.com/pipixue-wap/2020-1230-1107-56/ti_inject-812ce.png)
About peptide unit, the correctstatementsinclude
A.
The basic unit that constitutes secondary structure of polypeptide chain .
B.
The two α carbons are in the cis configuration .
C.
The single bond to the α carbon can rotate freely .
D.
The relative positions of the two adjacent peptide units are independent of rotation of the single bonds on either side of the α carbon .