$A\rightarrow BCD$
a. $A.s=B.i+C.s$
This is L attributed SDD. Attributes of parent node can take values from their children
b. $A.s=B.i+C.s,$ $D.i=A.i+B.s$
A cannot have inherited attribute. Since, there is nothing present on the LHS of A. So this SDD is neither S attributed nor L attributed
c. $A.s=B.s+D.s$
A's synthesized attribute is a function of synthesized attributes of its children. This confirms to S attributed definition. Every S attributed SDD is also L attributed SDD
d. $A.s=D.i,$ $B.i=A.s+C.s,$ $C.i=B.s,$ $D.i=B.i+C.i$
In the rule B.i=A.s+C.s. Here B's inherited attributed is taking values from its right sibling C. This violates L-attributed definition which says that inherited attributes are limited to take values from its parents or left siblings only. Hence, this SDD is not L-attributed