Ming placed a zero in the number 590 because the digit 1 in 16 has a value of 10.
When multiplying by 10 (the value of the 1 in 16), you effectively shift the value of the first number (in this case, 59) one place to the left, which is why there is a zero added after 59 to create 590.
Therefore, the correct answer is: C. The digit 1 in 16 has a value of 10.