有几条语法题不太明白，请指教

1  The province of Alberta lies along three of the major North American flyways used by birds____between their winter and summer homes

A the migration  B migrating  C migrate D and migrat (答案是B，C为什么不行)

2 The symtoms of pneumonia, a lung infection, include high fever, chest pain, breathing difficult, and coughing

我知道为什么选difficult，但是为什么include也对呢？不是including才对吗？？

1.migrate是动词呀，by是介词，介词后面怎么能直接跟动词原形？？

2.把整个句子的主谓宾弄清，include在这里明显是作谓语。

哦，明白了，谢谢啊