Replace the underlined tense form with the correct option:
If you will work hard you will certainly succeed.
A) Work
B) Works
C) Worked
D) Have worked

Hint: Tense is a category that expresses time reference. Tenses are usually manifested by the use of specific forms of verbs. The main tenses are: past, present and future.

Complete step by step answer:
In this question we have to replace the underlined words with the correct tense. And that should be grammatically correct.
Option A) Work – is the correct answer because the first verb 'to work hard' is in the simple present tense, followed by the next verb "you will certainly succeed" in the simple future tense. Hence the future form "will work hard" must be replaced with the simple present form i.e. 'work'. Thus, this is the correct answer.
Option B) Works – is an incorrect answer because ‘works' is also in the simple present tense, but it's used when the subject is in the third person i.e. he/she works. The subject 'you' is in the second person, instead of third form. So, ‘works’ is an incorrect answer.
Option C) Worked – is an incorrect answer because 'worked' is in the past tense. But, the sentence ‘if you will work hard you will certainly succeed’ is a type 1 conditional, hence 'worked' is an incorrect answer.
Option D) Have worked – is an incorrect answer because ‘have worked’ is in the present perfect tense, which isn't used in conditionals. And, also 'to work hard' is in the simple present tense, so, to replace the underlined words our preference should be in simple present tense. Thus, have worked is an incorrect answer.

Thus, the correct option is (A).

Note:
The given sentence is a type 1 conditional sentence as it begins with 'if'. It states an unreal situation that is likely to happen. The simple past tense verb is used in a type 2 conditional sentence, followed by the second verb form in the present continuous form i.e. will be succeeded. Conditional 1 means it is possible and also very likely that the condition will be fulfilled. Form: If + Simple present, will future. For example: If I found her address, I would send her an invitation.
Conditional 2 means it is possible but very unlikely. Form: If + Simple past, Conditional 1. For example: If I found her address, I would send her an invitation.
Thus, in this question conditional 1 is used so, option A is the most appropriate answer as compared to other options.