Searching for "GDZ" (готовые домашние задания - ready-made homework) usually brings up resources like pobio.ru , where you can find answers to the 8th-grade biology workbook by Sonin and Sapin.

: Muscles often work in pairs (like the biceps and triceps); when one contracts, the other relaxes to produce movement at a joint.

: Bones are made of organic substances (which provide flexibility) and inorganic minerals like calcium (which provide hardness).

: Skeletal muscles (striated) are responsible for voluntary movements, while smooth muscles control internal organs and are involuntary.

If you are looking for specific answers to exercise numbers (e.g., A1, A2), platforms like pobio.ru provide detailed breakdowns of the training tasks for this specific textbook.