Answer : 1. "The latest assignment was explained to Lana by the manager."
Explanation :

The given sentence is in Active Voice. As per the given question, we have to change it to Passive Voice.
The structure of the given sentence is as follows:
Subject + V2 + Object. (Active Voice)
Subject (objective case) + was/were + V3 + Object (subjective case). (Passive Voice)
Example: Their cousin showed them some rare photographs.
(Active Voice) They were shown some rare photographs by their cousin.
(Passive Voice) The subject of the given sentence is 'The manager'.
The object of the given sentence is 'the latest assignment.
The subject will be put in place of the object and the object will be put in place of the subject.
And 'explained' will be changed into 'was explained'. Lastly, the preposition 'by' will be added.