Did you notice the following sentence in my essay on Wednesday?
Online courses are becoming a common feature of university education.
It might seem strange to mix a plural with a singular like this, but it's correct. The reason is that the courses are being grouped together as one feature. Look at some similar examples:
- Traffic jams are a feature of everyday life in modern cities.
- Online courses are a positive development.
- Electric cars are a good idea.
- Lower birth rates in America are an interesting trend.