How to union intermediate tables in Power Query?

Hi Power BI Gurus,

How to union intermediate tables in Power Query? My sample is as below:

I am crawling data from some web pages. For each page, there will be a table. But I do not want to do with that multiple times. Power query allows me to take all the different web table into some intermediate tables, but when I combine these tables, the error reported as: 

Expression.Error: we cannot convert type table to type list.
Details:
Value=[Table]
Type=[Type]

Here is my M codes (only the last step in let block reported error as above):

let
...

type_changed_1_1 = Table.TransformColumnTypes(提升的标题1,{{"日期", type date}, {"质量等级", type text}, {"AQI指数", Int64.Type}, {"当天AQI排名", Int64.Type}, {"PM2.5", Int64.Type}, {"PM10", Int64.Type}, {"So2", Int64.Type}, {"No2", Int64.Type}, {"Co", type number}, {"O3", Int64.Type}}),
type_changed_1_2 = Table.TransformColumnTypes(提升的标题2,{{"日期", type date}, {"质量等级", type text}, {"AQI指数", Int64.Type}, {"当天AQI排名", Int64.Type}, {"PM2.5", Int64.Type}, {"PM10", Int64.Type}, {"So2", Int64.Type}, {"No2", Int64.Type}, {"Co", type number}, {"O3", Int64.Type}}),
type_changed_1_3 = Table.TransformColumnTypes(提升的标题3,{{"日期", type date}, {"质量等级", type text}, {"AQI指数", Int64.Type}, {"当天AQI排名", Int64.Type}, {"PM2.5", Int64.Type}, {"PM10", Int64.Type}, {"So2", Int64.Type}, {"No2", Int64.Type}, {"Co", type number}, {"O3", Int64.Type}}),
type_changed_1_4 = Table.TransformColumnTypes(提升的标题4,{{"日期", type date}, {"质量等级", type text}, {"AQI指数", Int64.Type}, {"当天AQI排名", Int64.Type}, {"PM2.5", Int64.Type}, {"PM10", Int64.Type}, {"So2", Int64.Type}, {"No2", Int64.Type}, {"Co", type number}, {"O3", Int64.Type}}),
type_changed_1_5 = Table.TransformColumnTypes(提升的标题5,{{"日期", type date}, {"质量等级", type text}, {"AQI指数", Int64.Type}, {"当天AQI排名", Int64.Type}, {"PM2.5", Int64.Type}, {"PM10", Int64.Type}, {"So2", Int64.Type}, {"No2", Int64.Type}, {"Co", type number}, {"O3", Int64.Type}}),
type_changed_1_6 = Table.TransformColumnTypes(提升的标题6,{{"日期", type date}, {"质量等级", type text}, {"AQI指数", Int64.Type}, {"当天AQI排名", Int64.Type}, {"PM2.5", Int64.Type}, {"PM10", Int64.Type}, {"So2", Int64.Type}, {"No2", Int64.Type}, {"Co", type number}, {"O3", Int64.Type}}),
type_changed_1_7 = Table.TransformColumnTypes(提升的标题7,{{"日期", type date}, {"质量等级", type text}, {"AQI指数", Int64.Type}, {"当天AQI排名", Int64.Type}, {"PM2.5", Int64.Type}, {"PM10", Int64.Type}, {"So2", Int64.Type}, {"No2", Int64.Type}, {"Co", type number}, {"O3", Int64.Type}}),
type_changed_1_8 = Table.TransformColumnTypes(提升的标题8,{{"日期", type date}, {"质量等级", type text}, {"AQI指数", Int64.Type}, {"当天AQI排名", Int64.Type}, {"PM2.5", Int64.Type}, {"PM10", Int64.Type}, {"So2", Int64.Type}, {"No2", Int64.Type}, {"Co", type number}, {"O3", Int64.Type}}),
type_changed_1_9 = Table.TransformColumnTypes(提升的标题9,{{"日期", type date}, {"质量等级", type text}, {"AQI指数", Int64.Type}, {"当天AQI排名", Int64.Type}, {"PM2.5", Int64.Type}, {"PM10", Int64.Type}, {"So2", Int64.Type}, {"No2", Int64.Type}, {"Co", type number}, {"O3", Int64.Type}}),
type_changed_1_10 = Table.TransformColumnTypes(提升的标题10,{{"日期", type date}, {"质量等级", type text}, {"AQI指数", Int64.Type}, {"当天AQI排名", Int64.Type}, {"PM2.5", Int64.Type}, {"PM10", Int64.Type}, {"So2", Int64.Type}, {"No2", Int64.Type}, {"Co", type number}, {"O3", Int64.Type}}),
type_changed_1_11 = Table.TransformColumnTypes(提升的标题11,{{"日期", type date}, {"质量等级", type text}, {"AQI指数", Int64.Type}, {"当天AQI排名", Int64.Type}, {"PM2.5", Int64.Type}, {"PM10", Int64.Type}, {"So2", Int64.Type}, {"No2", Int64.Type}, {"Co", type number}, {"O3", Int64.Type}}),
type_changed_1_12 = Table.TransformColumnTypes(提升的标题12,{{"日期", type date}, {"质量等级", type text}, {"AQI指数", Int64.Type}, {"当天AQI排名", Int64.Type}, {"PM2.5", Int64.Type}, {"PM10", Int64.Type}, {"So2", Int64.Type}, {"No2", Int64.Type}, {"Co", type number}, {"O3", Int64.Type}}),

CombinedTable = Table.Combine(type_changed_1_1,type_changed_1_2,type_changed_1_3,type_changed_1_4,type_changed_1_5,type_changed_1_6,type_changed_1_7,type_changed_1_8,type_changed_1_9,type_changed_1_10,type_changed_1_11,type_changed_1_12)

in 
CombinedTable