Direction: Which one is the most effective word(s) from the given words to fill in the blank to make the sentence meaningful? I shall not be late for dinner __________

'Unless' already carries the negative sense (= if not), and in a conditional clause about the future the simple present is used: 'I shall not be late for dinner unless the train is late.' 'Unless the train will be late' wrongly uses 'will' in the unless-clause, 'unless the train will not be late' adds both 'will' and a double negative, and 'if the train is late' reverses the meaning.