Определите видовременную форму глагола-сказуемого:
1. Man has always adapted himself to new conditions and new times.
2. Several interesting things happened while the ice was forming and while primitive men were developing in the Old World.
3. Historical studies have differed and will continue to differ about the dates of the periods of history.
4. The English had learnt from the Danes to use horses to move swiftly from place to place.