16 since pre-Hispanic times, Lake Catemaco has been a centre for alternative medicine and strange treatments.
答案：(A) Ever
【句型】Ever since + 時間點，固定搭配，表示「自……以來一直」，符合「卡特馬科湖自前西班牙時期以來就一直是……中心」的語意。Not／Only／Rarely 都不能這樣修飾 since 構成「自從……」的意思。
ever 這個字，你的印象大概只有疑問句與否定句裡的「曾經」（Have you ever been to Japan?），不太會想到它可以擺在 since 前面加強語氣。
鑑別度只有 34。這一格連高分群考生也常失手，原因就在 ever 的這個用法平常很少被單獨拿出來教——越熟悉 Have you ever ... 那個 ever 的人，越不會想到它能放在 since 前面。先看形態：主要子句是 Lake Catemaco has been a centre for alternative medicine（現在完成式），而 since pre-Hispanic times 標出起點。現在完成式配 since 起點本來就成立，空格要填的是一個能加強「一直持續」的字，那就是 ever。ever since 是成組的說法，意思是「自從……以來一直」。填進去讀成 Ever since pre-Hispanic times, Lake Catemaco has been a centre for alternative medicine（自前西班牙時期以來，卡特馬科湖一直是另類醫療的中心）。
Not、Only、Rarely 都是否定或限定的字，填進去會把整句變成否定或設限，與後面「一直是……中心」的肯定敘述矛盾；而且 Only 與 Rarely 放在句首時主要子句要倒裝，本句沒有倒裝，形態上就先出局——這一招在句首否定副詞的題目裡幾乎每次都用得上。
ever since ＋ 時間點（自從……以來一直）、since ＋ 時間點 ＋ 現在完成式（自……以來）、Only ＋ 副詞片語 ＋ 主要子句倒裝（只有……才）、rarely（很少，否定副詞）、converge on（聚集到某地）、alternative medicine（另類醫療）。
Every year Catemaco, a small town in the south of Mexico, hosts the Annual Witch Gathering. Healers and witch doctors converge on this beautiful lakeside town in March to make their yearly trade. 16 since pre-Hispanic times, Lake Catemaco has been a centre for alternative medicine and strange treatments. 17, the area's association with witchcraft dates back to Olmec times more than 2,000 years ago.
If you've ever seen the Sean Connery movie Medicine Man, 18 the annual convention of wizards and witches will be familiar to you. 19, get prepared for the overwhelming attack of wizards and witches here.
Most witch doctors are guaranteed to be charlatans, not real doctors, who 20 some quick money from tourists. Yet, don't be surprised if the occasional remedy offered is effective.