What Was the Explanation Given for Why Unrelated Children Raised

What was the explanation given for why unrelated children raised together in an Israeli kibbutz never married one another?

A) They simply didn't have very much in common with each other, which reduced attraction significantly.
B) There were strong social norms prohibiting children raised in the same pod from marrying.
C) Children raised together were close during childhood but grew apart in adulthood.
D) They developed a natural aversion to sexual relationships with each other as if they were siblings.