Variable product issue

Dear Support team,
First for all, thanks for awesome plugin. I has issue with variable product
When i add variation ( ex: color and size in single product ) and in the frontend, i cannot choose color and size for this product. I have used Woocommerce plugin v2.5.5 and wordpress v.4.5.2. Please check link below

https://www.dropbox.com/s/9wqkqjf0xnise9v/Screenshot%20%28558%29.png?dl=0

https://www.dropbox.com/s/o17gvo22u19ggrb/Screenshot%20%28559%29.png?dl=0

-Thanks you so much

https://ww.wp.xz.cn/plugins/woocommerce/