Epidemiology question involving directed acyclic graphs (DAG) and confounders

a. Assume that maternal education level affects the likelihood that a woman smokes while she is pregnant. In tern, material smoking during pregnancy affects the risk that their infant will have a low birth weigh. Is maternal smoking during pregnancy a confounder of the association between maternal education and low birth weight?
b. A study investigates whether surfing after rain storms increases surfers’ risk of diarrhea. Chronic gastrointestinal conditions (e.g., Celiac disease) affect the probability that a surfer will have diarrhea and may also affect a surfers’ choice of when to surf and how often to surf. Are chronic gastrointestinal conditions a confounder of post-rain storm surf exposure and diarrhea risk?
c. A randomized trial assesses the impact of school-based hand-washing education on the risk of intestinal worm infection. The trial successfully completes randomization of participants to intervention or control. Age is a predictor of intestinal worm infection. Is age a confounder of the relationship between the intervention and intestinal worm infection?