The correct answer is:
(a) True
It is true that predicting sites for posttranslational modifications (PTMs) based on protein sequences can be challenging, particularly because the sequence motifs associated with certain modifications are often very short. These short motifs make it difficult to reliably predict where modifications like phosphorylation, acetylation, or glycosylation might occur, as they may not be immediately obvious within the broader protein sequence. This is why bioinformatics tools often rely on additional contextual information, such as evolutionary conservation, structural data, or experimental evidence, to improve prediction accuracy.
So, the answer is (a) True.