The unknown compound has molecular formula $C_5{H}_{10}{O}_2.$ In addition, its IR$,1HNMR,13CNMR,$ DEPT$-90,$ DEPT$-135$ are listed below. Please answer the following questions:

$($A$)$ How many $1(C{H}_3),2(C{H}_2),3(CH),4(C)$ are there for the unknown respectively?

$($B$)$ Determine the structure of the unknown.