Given function Multiply $(u,v)$ that returns $u^{**}v,$ and Add$(u,v)$ that returns $u+v,$ which expression corresponds to Add$(ltiply(x,$Add$(y,z)),w)$

a$.(x^{**}(y+z))+w$

b$.(x+(y+z{)}^{**}w)$

c$.((x^{**}y)+z)+w$

d$.(x^{**}(y+z{)}^{**}w)$