中国大学MOOC: Old people, who risk vitamin D deficiency, should spend even longer exposed to （10） daylight.
举一反三
- 中国大学MOOC: what is the current prophylactic dosage of vitamin D for full-term breast feeding baby to prevent vitamin D deficiency?
- People should spend about 10 minutes ____________ with a 15-minute presentation.
- Who should be blamed for students' language deficiency?
- 中国大学MOOC: From daylight, our bodies absorb vitamin D through the skin. Certain skin diseases also （2） from exposure to sunlight.
- 中国大学MOOC: Nuclear testing has exposed millions of people __________ radiation.