The correct option is
C try
The given sentence is a Type 1 conditional, because it presents a possible condition (if-clause) and its probable result.
In
such sentences, the if-clause is in simple present tense and the main
clause is in the simple future tense 'You will succeed".
Option C: 'Try' is in the simple present
tense. It completes the sentence in meaning as well as agrees with the
Type 1 structure. Hence option C is correct.
Option A: 'Are trying' is in the present continuous tense. It isn't used in the first conditional.
Option B: 'Will try' refers to the future tense. It isn't used in the if-clause, but the main clause.
Option D: 'Are going to try' refers to a future action, whereas a present action is required.
Hence options A, B and D are incorrect.