input: Please answer the following: What is the missing first step of the following process: - Two types of proteins exist in filaments in the muscles - The filaments move when the brain instructs them to - The motion of the filaments cause the muscle to shorten and contract - Opposing pairs of muscles exist in order to provide the necessary range of motion.
++++++++++
output: Electrical signals in the brain travel through nerves to muscles

input: Please answer the following: What is the missing first step of the following process: - Nephrons in the kidney filter the blood - The waste that is filtered out mixes with water - Become urine - Ureters carry urine out of the kidneys.
++++++++++
output: Blood carried into kidney by the renal artery

input: Please answer the following: What is the missing first step of the following process: - Air enters bronchioles - Bronchioles have tiny air sacs called alveoli - Alveoli surrounded by small blood vessels - Oxygen absorbed by small blood vessels - Vessels deliver oxygen to every cell in the body - Blood brings carbon dioxide back to lungs - Carbon dioxide released when you exhale.
++++++++++
output: Air enters the lungs through bronchial tubes

input: Please answer the following: What is the missing first step of the following process: - The virus attaches to the cell's surface - The cell swallows the virus - The virus' RNA is released into the cell - The cell mistakenly reads the virus' RNA instead of its own - The cell creates new viruses - The animal cell releases the new viruses - The new viruses can infect more cells.
++++++++++
output:
The virus finds an animal cell