Someone who is highly trained in distinguishing different faces might still make occasional mistakes when presented with a particular face. how might this be explained by stimulus sampling theory?

According to the William Estes's stimulus sampling theory, each stimulus (in this case, faces) are made up of a variety of elements. As these faces are learned, part of these elements are randomly sampled on each trail, and only sampled elements can be associated with the response. Sometimes, it may occur that, on a particular trial, a subset of elements (that are not strongly linked to the correct response) is activated. Consequently, it leads to an error.    

this statement is true.

forests are public goods, available for everybody. when usage of such a good becomes interesting for consumers and its usage increases, there can be a risk of overexploitation. it is a non rival good therefore, if one person consumes the good it does not reduce the availability for subsequent consumers.

these caracteristics require the establishment of measures in order to prevent the destruction of a commonly owned space, for example, to restrict the amount of people that have access to the same time.