In what way are the humerus and the femur similar? a. they both attach their respective limbs to the axial skeleton. b. they both have similar joints at each end. c. they both are extremely strong and made only of compact bone. d. they both have hollow spaces filled with bone-generating cells. e. they both protect vital organs.

The humerus-
A long bone of the upper forelimb. It articulates proximally with the scapula to form the soulder joint and distally with the radius and ulna to form the elbow joint.
Proximally the humerus has a rounded projection known as the head. 

Cranially at the lateral aspect of the head is a large prominence- the greater tubercle. The lesser tubercle lies medially. Both tubercles act as a sight for muscle attachment. At the distal end of the humerus is a condyle which articulates with the radius & ulna & forms part of the elbow.

The diaphysis of the humerus is twisted.
In the dog a supra condylar foramen is present- a large hole in the condyle.

The Femur-This is the thigh bone and is the largest bone in the body, it is a long bone and is similar in structure to the humerus in that it has a head, neck, shaft & lateral & medial condyles. The femoral head articulates with the acetabulum proximally to form the hip joint, lateral to the head is the greater trochanter and on the medialTh side is a lesser trochanter (for muscle attachment). At the distal end of the femur are 2 condyles that articulate with the tibia to form the stifle joint. Between the 2 condyles is the trochlear groove along which the patella can move.

Here is some information. Hope this helps ☺