After the invasions began, european landowners found protection by entering into
a. feudal arrangements.
b. mercenary contracts.
c. land and sea watches.
d. sovereignty agreements.

A. feudal arrangements is the correct answer.

Explanation:

ww1 weapons: tank. tanks were used for the first time in the first world war at the battle of the somme. they were developed to cope with the conditions on the western front. the first tank was called 'little willie' and needed a crew of 3.