The phrase "are commonly difficult to" is correct and usable in written English.
It can be used when discussing something that is often challenging or hard to accomplish.
Example: "These tasks are commonly difficult to complete within the given timeframe."
Alternatives: "are often hard to" or "tend to be challenging to".
Therefore, it is commonly difficult to diagnose BHD only on the basis of histopathological findings of resected bullas [8].
PTE is commonly difficult to treat with drug therapy, and antiepileptic drugs may be associated with side effects.
Recent studies, however, have shown that it is commonly difficult to achieve adequate nutrition via the enteral route in critically ill patients [ 2, 3].
Fingerstick blood collection would also be of immense value in several types of subjects where it is commonly difficult to collect venous blood via venipuncture: infants and young children, intravenous drug addicts, and very obese individuals.
However, it is often questioned whether a truly quantitative RT-PCR method can be consistent among many laboratories, as it is commonly difficult to optimize and interpret [ 41, 44, 45].
As shown by several examples from arid and semi-arid regions, lives have been altered by rapid changes in landscapes, but separating human causes that may be manageable from non-human drivers that may not is commonly difficult.
46– 48 Whereas nutrition is commonly difficult from the beginning in patients with SMA type I, the difficulties are less frequent and constrictive in the other SMA types.
Some video lessons described Renewable Energy on the field of Biotechnology Industrial, which is one of the topics that commonly difficult to visualize and explain.
Moreover, the same types of instability can be induced by tangential follower forces, but these are commonly thought to be of extremely difficult, if not impossible, practical realization.
There are poor ergonomics, as lids and handles are commonly bulky, heavy, and difficult to grip.
