Question

Bones are hard structure and cannot be bend but we can still bend our elbow knee etc how is this pssible

Answer 1

we are not bending the bone. Knee is the place where two bone meet. The place where 2 bones meet is called a joint and it is flexible. So it is because of the joint that we are able to bend our leg, elbow etc...

Answer 2

bones are rigid but in certain points like the elbow and knee can bend because  they have hinge joints which help movement backward and forward.