3.20 Let X1, . . . , Xn be independent standard normal random variables. Determine the orders of the following sequences of random variables ξn:

(i) ξn = 
n i=1 Xi 
n i=1 X2 i 
n i=1 X3 i 
.
(ii) ξn = 
n i=1 Xi  
n i=1 X3 i 

1 +

n i=1 X2 i  
1 +

n i=1 X4 i  .
(iii) ξn = 
n i=1 X3 i 2 1 +

n i=1 X6 i .
(iv) ξn = 
n i=1 X2 i 4 1 +

n i=1 X8 i .