Final answer:
The correct expression for the number 45.623 is Option C: 45 ones + 6 tenths + 2 hundredths + 3 thousandths.
Step-by-step explanation:
The correct expression for the number 45.623 is Option C: 45 ones + 6 tenths + 2 hundredths + 3 thousandths.
When we break down the number 45.623, we can see that it has 45 ones, 6 tenths, 2 hundredths, and 3 thousandths. So, Option C is the correct expression.