A two-hinged semicircular arch of radius 'R' carries a concentrated load 'W' at the crown. The horizontal thrust is

• A. <img src="/_files/images/civil-engineering/upsc-civil-service-exam-questions/54-341-1.png">
• B. <img src="/_files/images/civil-engineering/upsc-civil-service-exam-questions/54-341-2.png">
• C. <img src="/_files/images/civil-engineering/upsc-civil-service-exam-questions/54-341-3.png">
• D. <img src="/_files/images/civil-engineering/upsc-civil-service-exam-questions/54-341-4.png">