Помогите плиз поставить глаголы правильную временную формуWhile reading the text open

Помогите плиз поставить глаголы правильную временную форму

While reading the text open the brackets putting the verbs into Past Simple Active or Passive.
The Fall of the Roman Empire
The Romans (to remain) in Britain for about four centuries and during that time Britain
(to be) a Roman province governed by Roman governors and protected by Roman legions.
In the 3rd-4th centuries the power of the Roman Empire gradually (to weaken). The
unproductive labour of the slaves (to lead) to the economic decline of the empire. Neither new
methods of land cultivation nor new technical inventions (to introduce). Slavery (to become) an
obstacle to technical progress. Poor cultivation (to exhaust) the fields, the harvests (to become)
poorer from year to year.
The uninterrupted struggle of the exploited against the slave-owners greatly (to weaken)
the Roman Empire too. The enormous number of slaves (to present) a great danger to the Roman
Empire. The end of the 4th Century (to find) the German tribes invading the Western Roman
Empire and the slaves who (to hate) the Roman state were joining them by the thousand.
Early in the 5th Century (407) the Roman legions (to recall) from Britan to defend the
central provinces of the Roman Empire from the attacks of the barbarian tribes. They (not to
return) to Britain, and the Celts (to leave) alone in the land.