B) esta. esta typically refers to describing something like location whereas es describes the person's attributes. (ie, esta would be used with "she is in the store" and es would be used with "she is cute"
You probably need to conjugate 'esquiar' to ustedes form but that depends on the form you guys are in like: Present or Past Pogressive, Preterite...etc.
Carlos es un chico muy _Bueno____.
