血吸虫侵染人体之前，会寄生在某种软体动物体内，这种软体动物是（    ）

增加：在缺词处加一个漏字符号（∧），并在其下面写出该加的词。

删除：把多余的词用斜线（\）划掉。

修改：在错的词下划一横线，并在该词下面写出修改后的词。

注意：1).每处错误及其修改均仅限一词；

2).只允许修改10处，多者（从第11处起）不计分。

    Last Saturday I took bike trip to the nature park together with three of my friends in the breeze (微风), there we went for sighting. In the forest, we saw a number of plant and knew a lot about them. And then we go to a patch of grass that was full of wild flowers. We lay in the sun quietly, enjoyed the fresh air. The sight was very amazing that we didn't want to leave. We talked about our experiences happy and played several childhood games. Later, we had photos taken together and rode back to home.

    It was really an unforgettable weekend because they learned a lot about plants. With addition, we relaxed ourselves by enjoying the beauty of nature.

阅读下列材料并结合所学知识，回答问题。

材料：《唐六典》记载唐王朝曾与三百多个国家和地区交往，每年都有大批外国客人来到长安。唐王朝设有专门机构（鸿胪寺、礼客院）负责接待外宾，设置翻译人员，提供各种便利。唐朝高度发达的经济和文化，对很多国家很有吸引力。波斯（伊朗）曾不断派遣使者前来长安，波斯商人遍布长安、洛阳、广州、扬州等地；唐朝从贞观年间开始，日本来中国的遣唐使有十多批，同来的还有留学生和留学僧等；新罗仿唐制建立了政治制度，采用科举制选拔官吏，还引入了中国的医学、天文、历算等科技成就。

﹣﹣摘编自《中国历史教师教学用书》

请回答：

根据材料并结合所学知识，概括指出唐朝对外交往活跃的表现。简析唐朝对外交往活跃的原因。