Let's evaluate each variable:

(a) Temperature (in degrees Celsius)

• Quantitative
  Temperature is a measurable quantity that can take a wide range of numerical values, making it a quantitative variable.

(b) Duration (in minutes) of a call to a customer support line

• Quantitative
  Duration refers to a numerical value (minutes), which is measurable, hence it is a quantitative variable.

(c) Dosage (in milligrams) of medication

• Quantitative
  The dosage is a numerical value (milligrams) that can vary, so it is quantitative.

(d) Native language

• Categorical
  Native language is a classification, not a numerical value. It groups people into different categories (e.g., English, Spanish, etc.), making it a categorical variable.

Final Summary:

• (a) Temperature: Quantitative
• (b) Duration: Quantitative
• (c) Dosage: Quantitative
• (d) Native language: Categorical

Would you like more details on any of these? Here are a few related questions for you:

1. What is the difference between continuous and discrete quantitative variables?
2. Can a categorical variable have an order or ranking? (What’s an example of an ordinal variable?)
3. Why is it important to differentiate between quantitative and categorical variables in data analysis?
4. Can categorical variables be measured in numerical terms? (Think of "codes" for categories)
5. How do qualitative variables help in grouping data?

Tip: Remember, quantitative variables always represent a measurable amount or count, while categorical variables represent different categories or groups.