Statement (a) is not correct. Skeletal muscles are of course connected to the bones, hence the name. So (d) is correct. They are also surely used to move large parts of the body and are necessarily controlled by the central nervous system, i.e. the brain and spinal chord, just like everything else in the body. Therefore statement (a) is not correct, the skeletal muscles do not control involuntary body functions (though this could be said to be true in some cases, for example the knee-je.rk reaction.)
