The season that is starting is winter.
The answer to 21 is (4)
People who work with radioactive materials often wear a film badge to reveal how much radiation they have been exposed to. The film badge dosimeter or the film badge is a dosimeter worn by these people working with materials that are radioactive for the purpose of monitoring cumulative radiation dose due to ionizing radiation. The badge has two parts; the photographic film, and a holder.
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Here is the link to a great video that explains your question nicely, hope this helps.
The third one
synthesis reactions have multiple reactants that synthesize into one product
