Two-ports question ABCD parameters
Using the definition:

$$ A = \frac{v_i}{v_0}\mid i_0=0 $$
$$ B = \frac{v_i}{i_0}\mid v_0=0 $$
$$ C = \frac{i_i}{v_0}\mid i_0=0 $$
$$ D = \frac{i_i}{i_0}\mid v_0=0 $$

Output voltage is voltage over R
$$ A: v_0 = \frac{R}{R+jx}v_i \Rightarrow A = \frac{R+jx}{R} \\ $$
Input voltage is voltage over jx + voltage over R
$$ B: v_i = i_ijx + (50+1)*i_iR 
 = i_0\frac{jx}{50} + i_0\frac{51}{50}R $$
$$ v_i = \frac{jx+51R}{50}i_0 \Rightarrow B = \frac{jx+51R}{50}  $$
Output voltage is voltage over R
$$ C: v_0 = i_iR \Rightarrow C = \frac{1}{R}$$
Relation is already given
$$ D: i_0 = 50i_i \Rightarrow D = \frac{1}{50} $$

Assuming that when $$i_0 = 0 $$ the current source cannot deliver any current.