$32$ bit hierarchical carry$-$lookahead adder$.48$ bit carry$-$lookahead adder$.$

The following figure shows the structure of a $32-$bit hierarchical carry$-$lookahead adder. In this structure, four $8-$bit carry$-$lookahead adders are used.

$.2$ bit carry$-$lookahead adder$4$ bit hierarchical carry$-$lookahead adder$..$ second$-$level lookahead$$ AND$$ OR $.$

Using this method, implement a $4-$bit hierarchical carry$-$lookahead adder using two $2-$bit carry$-$lookahead adders. Express the gate circuit for the second$-$level lookahead with AND and OR gates.