Flags have existed for over 3,000 years. The earliest flags were wooden or metal poles with a carving. About 2,000 years ago pieces of fabric were added to some poles for decoration. Over the next 500 years the free-flying part of the flag became more important.

甲用沾有面粉的手与乙握手，这一过程可以模拟传染病的传染过程．这个模拟活动中，相当于病原体和易感人群的依次是（    ）

【旅游地理】阅读材料，完成下列问题。

赛里木湖位于天山西段的高山盆地中，被称为大西洋的最后一滴眼泪，是新疆面积最大的高山冷水湖。湖四周的倾斜低岸，水草丰美，为优良牧场。游客大多选择夏季来此游玩。

说明赛里木湖夏季吸引游客的原因。