This is the 15021st most frequent Russian word.
подходящие
Suitable.
The word 'подходящими' (appropriate/suitable) describes the books as fitting or proper for a particular purpose, in this case, studying history.
Эти книги являются подходящими для изучения истории.
These books are suitable for studying history.
Here, 'подходящие' refers to solutions that are suitable, appropriate, or adequate for addressing the complexity of this situation.
Мы должны найти подходящие решения для этой сложной ситуации.
We must find suitable solutions for this difficult situation.
The use of 'подходящим' (suitable) evaluates the training as potentially not fitting or appropriate for beginners.