I believe the correct answer is exercitui. You need the perfect passive form here, which is formed when you combine the verb esse in the present tense (here, sunt because of third person plural), and the appropriate participle in the same person, which in this case is exercitui - third person plural.
This is romanian Formulate a assert in which to specify the following aspects of the given text: the southern boundary of the Banat mountains, the area in which the sedimentary of the getic domain is well represented.
