The phrase "are mostly short" is correct and usable in written English.
It can be used to describe a general characteristic of a group or category, indicating that the majority of items in that group have a short length or duration.
Example: "The responses to the survey are mostly short, making it easier to analyze the data quickly."
Alternatives: "tend to be brief" or "are generally concise."
The site is dotted with water points and pit latrines; queues are mostly short.
While Angus is a thrilling soloist (at least on those early records where his breaks are mostly short, sharp and shocking), Malcolm was all accent, drive and reinforcement.
They are mostly short herbaceous perennials, many of which are tufted or mat-forming hardy evergreens, often with very showy flowers.
A brace of chiming acoustic love songs highlights singer Sam Forrest's writing skills, though the pleasures of NBA (the name comes from a line in a Sylvia Plath poem ) are mostly short, sharp and dark.
The poems in the best recent anthology, The Rattle Bag, are mostly short, accessible, and good – even though some of them might not meet the Gove criterion of being British.
Its 23 principal tributaries, which include the Passumpsic, White, Deerfield, and Farmington rivers (on the right) and the Ammonoosuc and Chicopee rivers (on the left), are mostly short, swift streams in narrow valleys dotted with small power dams, storage ponds, and factories.
Particles of the second and third generations are mostly short-lived and so rarely found outside particle-physics laboratories, though they were common at the beginning of the universe.
Although, vemurafenib, a BrafV600E specific inhibitor, showed impressive results in terms of response rate and progression free survival, the responses are mostly short-lived as seen by development of resistance in nearly every case [ 23- 25].
There are a few observations after examining those terms: the majority of them are lipid related; those terms with BP− and MF− class label are mostly short-chain lipids, which are not considered as lipid in our curation rule; some of the 15 BP? and 1 MF? are indeed lipid-related terms we miss, and they belong to the category of difficult-to-find term mentioned in the previous paragraph.
As can be seen in Fig. 5, the search times for individual observers are mostly shorter than their mean dominance durations.
In routine laboratory procedures refrigerated storage periods are mostly shorter and thus do not need to be considered as a critical parameter.
