sentence2_structure: The development of the respiratory system in the fetus<>begins<>at about 4 weeks
sentence1: Normally the XY chromosome fetus (male) automatically develop testes in the seventh week of development, and they in turn produce the male hormones that immediately begins to develop a male brain and other male features.
sentence2: The development of the respiratory system in the fetus begins at about 4 weeks.
question: The development of the respiratory system in the fetus begins at about?