[tex]\text{Intr-un paralelogram, doua unghiuri vecine sunt suplementare.} \\
B = 2 C \\
B + C = 180^o \\
---------- \\
2C + C = 180^o \\
3C=180^o \\
C = 180 : 3 = \boxed{60^o} \\
B=2C=2 \ times 60 = \boxed{120^o} \\
A = C = \boxed{60^o} \\
D = B = \boxed{120^o} \\[/tex]