No, Tom, it cannot be seen that way. It depends on the meaning. If 'pre-' is a prefix and means 'before', then it is pronounced /pri:/, but in cases like 'precious' (where no prefix is involved at all), or in cases where the meaning 'before' has become vague or lost (as in 'prefer'), other factors (stress pattern, origin, etc) will more likely affect the pronunciation.
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