My mother, along with others, . . . . . . . . worried.

The verb in the statement should agree with the subject of the statement.
For singular subjects, singular verbs are used and for plural subjects, plural verbs are used.
Here, the subject is 'my mother', which is singular. Hence, the verb used can be 'was' or 'is'.
But, in the options, 'is' is not given. Hence, the correct answer is option D.