[单选题]
Assuming the lower arm ha n-:8xhu 5m0no myygs3s a ma q7ms3-gb 8(kyv p3oyn -won-bss of 2.8 kg and its CG is 12 cm from the elbow-joint pivot, hkbqbv-on8(n-m7 3 y-3sygowp ow much force must the extensor muscle in the upper arm exert on the lower arm to hold a 7.5 kg shot put (Fig. 9-1)?
