(a) Here is a list of fifteen foods that boost the immune system: https://www.healthline.com/health/food-nutrition/foods-that-boost-the-immune-system
(b) Here are three Grokker programs that you might enjoy:
Honestly Healthy with Natasha Corrett https://grokker.com/cooking/nutrition-101/program/honestly-healthy-six-day-cleanse/5501d5dbe7ad06765109d89a
Healthy and Delicious with Danielle Hayley https://grokker.com/cooking/nutrition-101/program/healthy-and-delicious-with-danielle-hayley/577d6f0ab8b2904156e86b0a
Quick and Healthy Meals https://grokker.com/cooking/party-and-entertaining/program/quick-and-healthy-meals/55075ef7ea93175978a3598d
(c) Here is a collection about Healthy Nutrition: https://grokker.com/cooking/collection/healthy-nutrition/603ad327b356ab7d31b48ff0
Best wishes! :)