The correct option is B Add, will taste
A sentence that begins with 'if' is a conditional. These sentences refer to hypothetical situations, 'what could happen' and 'what we wish would have happened'.
The given sentence is also a conditional. It's a type 1 conditional, which means that the if-clause is a possible condition (add tomatoes) and the main clause is its probable result (the sauce will taste better). In this type, the tenses used are:
if-clause (simple present) + main clause (simple future)
Option B: The verb 'add' is in the simple present, and 'will taste' is in simple future. It adheres to the requirement for type 1 conditional. Hence B is the correct option.
Option A: 'Add' and 'taste' both are in simple present tense. The latter has to be in future tense.
Option C: Similarly, both the tenses 'will add' and 'will taste' refer to the future, but that isn't correct. The if-clause refers to the present action.
Option D: 'Will add' refers to the future and 'taste' refers to the present. But, as mentioned above, the condition (if-clause) cannot be in the future, leaving the result (main clause) in the present.
Hence options A, C and D are incorrect.