The phrase "are mostly common" is not correct in standard written English.
It can be used when discussing the frequency or prevalence of something, but the phrasing is awkward.
Example: "These types of errors are mostly common in beginner-level programming."
Alternatives: "are quite common" or "are generally common".
The rules are mostly common sense, but strictly observed, as if a children's summer camp had suddenly been invaded by mature, scrupulously careful Eagle Scouts.
This chapter highlights seven content bloopers that are mostly common and may invite serious damages to the purpose of a Website.
Genetic predictors of drug efficacy are mostly common variants with a range of effect sizes; most have been discovered through studies of sensitive quantitative measures of drug response, and all but one were discovered following drug approval.
Mucosal inflammation and ulceration occur throughout the gastrointestinal tract and are mostly common in the ileocecal region [40, 41].
In the 2nd phase of the study, only IC3 and IC4 conditions were considered since these conditions are mostly common in construction sites of the country.
Most of the pastures for reindeer and free-ranging sheep in Norway consist of harsh mountain ranges that are mostly common lands.
In fact, it's mostly common sense -- and above all it's reassuring.
Polydrug use is mostly common among adolescents and young adults, often with the intention of enhancing or counteracting the effects of another drug.
The way to do this, it suggests, is to give more space to pedestrians as well as to cyclists and public transport.This is mostly common sense.
At the end of last year Industrial and Commercial Bank of China (ICBC) displaced Bank of America to become the world's biggest bank by Tier-1 capital, which is mostly common stock and retained earnings.
