Some consumers who wish to support sustainable agriculture will only buy produce if it is certified and labeled as 100% organic, while others believe that formal regulation can be bypassed by building trust between producers and consumers.
A) only buy produce if it is certified and labeled as 100% organic
B) buy produce only if it was certified and labeled as 100% organic
C) buy produce only if it would be labeled as 100% organic and certified
D) buy only produce if it were labeled as 100% organic and certified
E) buy produce if it would only be labeled as 100% organically certified
Ans: Lets deconstruct this to understand meaning first.
Some consumers ( Main S)
who wish to support sustainable agriculture ( modify main subject. provide extra info about what type of consumers

)
will only buy ( Main Verb ) produce
if it is certified and labeled as 100% organic, ( If clause. S-> "it" (refer to the "produce" logically ) , V -> "is" )
while ( Dependent clause )
others believe ( SV pair of DC)
that formal regulation can be bypassed by building trust between producers and consumers. ( Clause informing us what other folks believe. )
Clauses structure (rearranging) : If clause, then Main Clause, while Clause that Clause.
We have then part is in future tense and is non underlined -> so is fixed. Now going back to rules: If X , Y clauses-> If X ( present tense ), Y ( present or future tense) -> in case of Real/ habitual or future certain scenarios. For details of such tenses construction refer to :
So logically and tense wise -> A seems fine and clear in meaning. Hold
B) buy produce only if it was certified and labeled as 100% organic
Placement of "only" now leads to meaning getting messy. "only produce" means Some consumers will buy produce only and nothing else. No milk and animal products

Unfair -> slight shift in meaning. But the bigger issue is the use of past tense in "if Clause" -> why would we want to talk about the "if" clause in past tense for the certain condition (fact/truth) happening in future. If we use past tense in IF clause we need to use Past tense in then clause to present past certain conditions/fact -> Eliminate.
C) buy produce only if it would be labeled as 100% organic and certified
"would" is used for hypothetical/uncertain/unreal condition. and "would" usage here is not correct in IF clause since then clause is in future certain condition. Placement of "only" similar issue like B. Other minor issue: "Labelled as certified" -> second part of the list is not as clear as A. Eliminate
D) buy only produce if it were labeled as 100% organic and certified
"were" is used in IF sentence (For technical folks : Past Subjunctive) so we need to use "would /could" in then clause. For hypothetical scenario we cannot use future fact/truth tense in "then" clause. Same issue "Labelled as certified" -> in list as in C. Eliminate
E) buy produce if it would only be labeled as 100% organically certified
"would" usage is wrong like option C. placement of "only" distort meaning compared to option A. I would not think too much about usage of "100% organically certified here." Eliminate.
Learning : IF X, Y -> IF Y is in future tense, X must be in simple present tense to present certain conditions for events to occur. Real conditional tense.