For each of the following cartoon representations from left to right, indicate whether the protein structure is composed of only ? helices (1), only parallel ? sheets (2), only antiparallel ? sheets (3), ? helices plus parallel ? sheets (4), or ? helices plus antiparallel ? sheets (5) as repetitive secondary structure elements. Your answer would be a four-digit number composed of digits 1 to 5 only, e.g. 5513.

Images created in PyMOL, from PDB entries 1STU, 2LPC, 1SA8, and 3BOB.