It was created 18 the format of XYX, with X being any number between 2-9 and Y being either 1 or 0.
答案：(D) in
in the format of 是「以…的格式」，in 表示「以某種形式、方式」；for（為了）、as（作為）、by（藉由某種方法）語意都不合。
答對率 28%。
中文的「以」在英文裡不只一個字：你看到「以 XYX 的格式建立」，直覺用 by（因為背過 by 表方法），結果選錯。關鍵在於 by 與 in 分工不同——by 表示「藉由什麼手段去做」（by bus、by hand、by email 寄送），in 表示「呈現出來的形式或樣態」（in English、in cash、in order、in this way）。格式是「呈現的樣子」，不是「動作的手段」，所以用 in。
It was created in the format of XYX——區碼是「長成 XYX 這個樣子」，接著整句還說明 X 是 2 到 9 的任一數字、Y 是 1 或 0，全都在描述外觀格式，不是在說用什麼工具去創造。
for the format 是「為了格式」，as the format 是「作為格式」，兩者都把格式當成目的或身分，語意不通；by the format 則會變成「藉由格式來創造」，因果顛倒。
國中學過 in English（用英文）、in pencil（用鉛筆寫）、in red（用紅色）——這些「用」其實都是「以某種形式呈現」，全部用 in，與 by bus 那種「交通手段」分屬兩類。
in the format of（以…的格式）、in the form of（以…的形式）、in English／in cash（用英文／付現）、by bus／by hand（搭公車／用手工）、in this way（用這種方式）。
An area code is a section of a telephone number which generally represents the geographical area that the phone receiving the call is based in. It is the two or three digits just before the local number. If the number 16 is in the same area as the number making the call, an area code usually doesn't need to be dialed. The local number, 17 , must always be dialed in its entirety.
The area code was introduced in the United States in 1947. It was created 18 the format of XYX, with X being any number between 2-9 and Y being either 1 or 0. Cities and areas with higher populations would have a smaller first and third digit, and 1 as the center digit. New York, being the largest city in the United States, was 19 the 212 area code, followed by Los Angeles at 213.
In countries other than the United States and Canada, the area code generally determines the 20 of a call. Calls within an area code and often a small group of neighboring area codes are normally charged at a lower rate than outside the area code.