Final answer:
The symbol that correctly completes the sentence '-10 _________ -3' is '<', making it '-10 < -3' because -10 is less than -3 when considering the order of negative numbers.
Step-by-step explanation:
The symbol that makes the sentence -10 _________ -3 true is the '<' symbol. This is because in the context of negative numbers, a number with a larger absolute value is considered to be less than a number with a smaller absolute value. In this case, -10 has a larger absolute value than -3, but since both numbers are negative, -10 is less than -3. Therefore, the correct sentence is -10 < -3.