Surfactant production in lungs stas at:

Alveolar type II cells first appear in the 17 to 26 weeks of gestation. They are the surfactant producing cells. However, the process of surfactant production must mature to become efficient at reducing surface tension. Mature, functional surfactant is produced by 34-35 weeks. Since the question is - "surfactant production begins at; the answer should be 18 weeks. It is the most appropriate answer. Extra edge Surfactant stas to appears in amniotic fluid between 28 and 32 weeks of gestation. By 20-24 weeks, primitive alveoli forms and surfactant production begins but it does not reach the surface of the lungs. Mature levels of pulmonary surfactant are present after 35 wk of gestation.