For prediction of three-dimensional structure of protein, P. homology modeling tries many possible alignments Q. threading first identifies homologues R. threading evaluates many rough models S. homology modelling optimises one model

The statement asks which statements are correct. P (homology modeling tries many possible alignments) is TRUE because homology modeling must test different alignments between the target and template to find the best structural fit. Q (threading first identifies homologues) is also TRUE because threading methods search structural databases to find potential homologous templates before threading the sequence. R is false (threading doesn't evaluate many rough models - it selects templates). S is false (homology modeling doesn't just optimize one model - it explores multiple alignments).