The clause element of adverbials, compared with other elements of a sentence, is relatively mobile, because it may occur initially as a sentential adverbial modifying the whole sentence, or occur finally as an information focus. But on the whole, its position is rather stable, usually appearing before the verb it modifies. A sentence may contain a varied number of adverbials, but adverbials are optional.
 Loar, J. K. (2011). Chinese syntactic grammar: functional and conceptual principles. New York: Peter Lang.