premise: How Your Baby Is Growing and Developing Your Baby's Nervous System The beginning of  the baby's nervous system (brain and other structures, such as the spinal cord) is seen as early as week 4 as the neural plate begins to develop.
hypothesis: The development of the respiratory system in the fetus begins at about 4 weeks.
hypothesis_graph_structure: The development of the respiratory system in the fetus<>begins<>at about 4 weeks