Spanish language Q&A Forum

I understand that the permanent-temporary rule is not a good one to use for “ser” and “estar”.  However a Spanish speaker told me that it is common to use “quedar” for the location of fixed items, such as buildings or roads, and “estar” for moveable items, such as people.  Is this correct?  Thanks.

One time when both I and my Spanish level were younger, I was visiting Guatemala and would often go to a particular restaurant for breakfast where I was always served by the same waitress.  We go to know each other and one day she told me all about her sister who worked nearby. 

The next day I wanted to be polite and ask how her sister was, so I asked, in error, "¿Cómo es tu hermana?" Immediately she frowned and walked away and never served me again, with the manager serving me instead. The only explanation that I can think of was that, in using the verb "ser" instead of "estar", I had really asked, "Is your sister hot?"   That is, how is your sister physically? So my question is, does saying "Como es..." ever refer to physical attributes?

'such as using renewable energy'

I put 'como usar la energia renovable' but was marked as incorrect with the correct option being 'como el uso de.. '

When ( if at all ) can I use an infinitive after como?

Gracias

I believe the word "en" is missing before the words "negra y blanca."