sentence2_structure: The development of the respiratory system in the fetus<>begins<>at about 4 weeks
sentence1: For example, a male's genes would begin to show the fetus as male (usually about 7 weeks) by developing testicles, scrotum and penis.
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?