Small changes in protein structure may lead to big changes in protein structures. A. secondary; tertiary
B. primary; secondary
C. primary; tertiary
D. tertiary; secondary

B. primary; secondary

Explanation:

Small changes in primary structure can result in large changes in protein shape and function. Secondary structure describes regions where the polypeptide is folded into localized shapes. There are two types of secondary structure (alpha helix and Beta pleated sheet).

the positions which points up in upward carbon and down in downward carbon are axial

and vice versa holds true for equatorial positions

so the correct answer with labelled diagram will be