expiration time problems on wordpress

Hi all,

I use the (awesome) W3-total-cache plugin for some time now. I think I have major speed issues on my website and testing websites agree with me.
I have some files in the website that don’t have expiration time and can’t figure it out.

I have the last version of wordpress and W3-total-cache

Perhaps could you help me on this issue?
Here is the report
https://developers.google.com/pagespeed/#url=http_3A_2F_2Fwww.lengrand.fr&mobile=false&rule=LeverageBrowserCaching

and the output I get on page speed :
“””
The following cacheable resources have a short freshness lifetime. Specify an expiration at least one week in the future for the following resources:
https://www.lengrand.fr/…/comment-bubble-dark.png (expiration not specified)
https://www.lengrand.fr/…/search.png (expiration not specified)
https://www.lengrand.fr/…/google-plus.png (expiration not specified)
https://www.lengrand.fr/…/linkedin.png (expiration not specified)
https://www.lengrand.fr/wp-content/uploads/2011/10/rss.png (expiration not specified)
https://www.lengrand.fr/…/twitter.png (expiration not specified)
https://www.lengrand.fr/…/viadeo.png (expiration not specified)
https://www.lengrand.fr/…/cropped-suommenlina.jpg (expiration not specified)
https://www.lengrand.fr/…/matlab_cl.png (expiration not specified)
https://www.lengrand.fr/…/region_growing.jpg (expiration not specified)
https://www.lengrand.fr/wp-content/uploads/2011/11/type.png (expiration not specified)
https://www.lengrand.fr/…/3d3cc2b2.5f721a.css (expiration not specified)
https://www.lengrand.fr/…/bf2af721.036786.js (expiration not specified)
https://www.lengrand.fr/…/icon_smile.gif (expiration not specified)
https://www.lengrand.fr/…/icon_wink.gif (expiration not specified)
https://connect.facebook.net/en_US/all.js (14.9 minutes)
https://apis.google.com/js/plusone.js (60 minutes)
https://www.google-analytics.com/ga.js (2 hours)
https://edge.sharethis.com/images/spinner.gif (21.6 hours)
“””
Any help would be greatly appreciated.

Thanks by advance !