Could you please provide the complete question and all the answer options .
That would make things a l'l easier , hope so!

budetta4 wrote:there has been a significant occurance of aok blight increase caused by growing fungus resitence against herbicides

B increase in the occurance of aok blight caused by growing fungus resistence againt
D increase in the occurance of aok blight because of growing fungus resistence againt

Correct Answer choice D But I chose B
Should I always prefer "because of" to "caused by" or there's a grammar rule to follow
Thanks in advance

Because Of versus Caused By

Typically you will see caused by directly after a form of the verb to be. Because of will occur after any other verb.

For example

Correct: The student was late because of his sister

Correct: The students lateness was caused by his sister.

So examine the verb right before the phrase and determine if it is a form of to be. In the first sentence above the the verb right before the phrase is "late" and thus because of is preferred. In the second, was (which is a form of to be) is right before the phrase and thus caused by is preferred.

In the question the verb "increase" is right before the phrase and thus because. IF the sentence read differently it could have a different wording. For example

Correct: there has been a significant occurrence of aok blight increase which was caused by growing fungus resistance against herbicides

Make sense?