<綜合測驗>第16至20題為題組 Street pigeons are a common sight in many European cities. In fact， a visit to a major European city just would not be the same ______ 16 ______ encountering them: bathing in fountains， perching on historic buildings， and flocking in public squares. In Barcelona， however， the birds are now threatening to ______ 17 ______ the city’s historic center， pooping on monuments， buildings， and even tourists. (A) as (B) for (C) though (D) without
