There are two hinged semicircular arches A,B and C of radii 5 m, 7.5 m, and 10 m respectively and each carries a concentrated load W at their crowns. The horizontal thrust at their supports will be in the ratio of

A

$$ 1 : 1 \frac{1}{2} : 2 $$ 

B

$$ 2 : 1 \frac{1}{2} : 1 $$ 

C

$$ 1 : 1 : 2 $$ 

D

None of these