Improve the bracketed part of the sentence.
(Be in the military) is grueling but satisfying.
The correct answer is option 3.
The given sentence is incorrect because the verbs ‘grueling’ and ‘satisfying’ are in the present continuous tenses but ‘be’ is not. Thus, converting ‘be’ into present continuous tense is the solution, which is option 3. Option 2 again uses simple present tense ‘goes’. The verb ‘go’ is also incorrect in option 1.
Hence the correct sentence is – ‘$Being in the military $is grueling but satisfying’.