**Explanation:** To find the significant digits in addition, the rule is we round off the result to the least precise input number. This simply means, to the number which has least decimal places. The input numbers are 1.513 and 27.3. Now 27.3 has 1 decimal place (less than 1.513, which has 3 decimal places), therefore, the result should also have 1 decimal place. Therefore, option B is correct.

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