Loading 1000 bags of cement into a truck is a fixed-work task. 

Gestation is a fixed-duration and fixed unit task. It takes 100% of one resource (fixed-unit) and 9 months (fixed-time) 

Burning 10.000 copies of a finished software is a fixed-work task.

Testing a process workflow may be a fixed-time task, if you have to actually wait for real events to happen (i.e.: accepting a purchase order, shipping and receiving the delivery confirmation)

Fixed-unit examples are harder to find, but usually are the tasks where you use a fixed percentage of a resource, as in the pregnancy example.