A series is given with one term missing. Choose the correct alternative from the given ones that will complete the series.7, 13, 21, 31, 43, 57, ?

Let's find the differences between consecutive terms:$13-7=6$$21-13=8$$31-21=10$$43-31=12$$57-43=14$ The differences are increasing consecutive even numbers: 6, 8, 10, 12, 14.The next difference must be 16.
$$\text{Missing term}=57+16=73$$