社会保障制度的核心是（     ）

请阅读下面短文，理解其大意，然后从每小题所给出的A、B、C三个选项中，选出一个能填入空白处的最佳选项。

    Maxime and Lise are a young French couple. They are ready to travel across China from Beijing to Yunnan Province on a tandem bicycle (双人自行车). They have two main purposes and one of them is that they want to encourage green 1 through it.

    Maxime, 26, works helping farmers raise their cows, 2his wife Lise, 26, is a teacher. The two also like sharing their travel stores on Facebook.

    We chose a tandem bicycle because it makes it 3 to communicate with each other about interesting people and things we come across during the journey. 4, bicycling is healthier. And it's a cheaper and more environment-friendly way of traveling than 5 cars, motors and so on, “the couple said.

    As for the other 6of their journey, the two said they wanted to get people's good ideas on topics such as health, econnmy (经济) and politics. When they were asked 7they chose to visit China, they said it was because they often talked about its long history and beauty and how much of the country is competitive (有竞争力的) in the world.

    We know China is a country with a large population and will be the 8 of the economy around the world in the future. We want to get a better understanding of the country and its people. We 9the country,” they said.

    The couple will be on the journey to China soon. We hope they can make more people further 10 China by shairing what they see and hear on the way. Meanwhile. We hope they enjoy their travel in China.