Umm is this like a school question or a normal question I mean you can just search it up
Answer:
D. is a hobby
Explanation:
According to my research on the English language, I can say that based on the information provided within the question the correct statement for this question would be "is a hobby". Therefore the whole correct sentence would be "Stamp collecting is a hobby sometimes used in the schools to teach economics and social studies."
I hope this answered your question. If you have any more questions feel free to ask away at Brainly.
Answer:
I think it's "They have a time-proven way of doing things."
