They didn't reach an agreement . . . . . . . . their differences.

In the given sentence, we need to choose the correct linker from the given options.
All four of them can be used in the blank. However, only option b follows the format of the sentence.
'Due' and 'owing' are followed by 'to,' which is not present in the sentence. 'Because' is followed by 'of,' which is again not present in the sentence. Thus, they will not be taken as the answers.
'On account of' consists of the preposition 'of' and is the complete answer.