They're also sectors that depend on a constant churn of people and goods entering and exiting borders.

The drought has come despite a constant churn of top-end Canadian talent, as well as men's gold in three of the past four Olympics.

This constant churn and movement is a real issue and I often worry that it undermines the institutional memory (and capacity) of departments.

Before her speech Hunter told the BBC that headteachers were also unhappy about the " constant churn of educational change" and negative rhetoric from the government.