Read the following passage and mark the letter A, B, C, or D to indicate the correct answer to each of the questions.

Scandinavia has ranked as the best place in the world to raise children. The Nordic region holds the top three places on the US News & World Report's list of "The Best Countries for Raising Kids" in 2020. The list has been compiled annually since 2016 in collaboration with the University of Pennsylvania. Denmark topped the list, with Sweden a close runner-up, and neighbour Norway edging out Canada for third place. The 2020 listings will come as little surprise as the three nations also ranked highest on the list for 2019. A spokeswoman explained: "These countries tend to have generous paternal leave and maternal leave, offer free preschool and have good overall public education systems."

The listing was released as part of the annual "Best Countries" list. This survey adopted "a global perceptions-based" approach in examining data and attitudes. It used research from the World Bank, as well as the opinions of 20,000 people in the Americas, Asia, Europe, the Middle East and Africa. Researchers tested countries against 65 different metrics, or what the researchers called "country attributes". These included income equality, well-developed public education and healthcare systems, human rights, gender equality, safety, family friendliness and levels of perceived happiness. Switzerland once again topped the "Best Countries" list, followed by Canada and Japan.

Several important methods were invented for _______________ food in the nineteenth century. A. protecting B. preserving C. saving D. preventing