A general understanding of grammar/sentence structure can help.
You can also make your own shuffled sentences - using easier sentences and Word.
There are a few in FPTP which are fiendishly difficult
This isn't a bad thing as for CEM exams, children need to be used to not being able to answer everything perfectly.
My dd had loads of practice on these (ones I made as the FPTP book has only just been published) and still wasn't that great at them. Fortunately although she lost masses of marks on this section, her comprehension, vocab, etc were good which got her the score she needed at the end. If your child is really struggling, another approach might simply be to ensure that the other areas are very solid.