一个直角三角形的三条边分别长3cm、4cm、5cm，这个三角形的面积是[     ]

A．6平方厘米    

B．10平方厘米    

C．12平方厘米

We work together to achieve our common purpose: _____ world that is safer, cleaner and healthier than _____

one we founded. [ ]

A. the; the

B. a; 不填

C. a; the

D. the; 不填