Since then, World Hello Day—November 21st of every year— 27 observed by people in 180 countries.
答案：(B) has been
現在完成式被動語態 has been，配合 Since then（從那時起，表持續到現在），「一直被180個國家的人們觀察/慶祝」；is（現在簡單式，不符合持續性）、was（過去簡單式，不符合持續到現在的語意）、had been（過去完成式，沒有更早的過去參照點）都不合。
看到 Since then 你大概馬上想到完成式，這一步不難。真正會失手的地方有兩個：一是被兩個破折號中間那一大串卡住，找不到主詞；二是沒注意到 observed 是過去分詞，這裡需要的是被動語態，不只是時態。
先把破折號中間的插入語拿掉。World Hello Day—November 21st of every year—______ observed by people in 180 countries. 兩個破折號夾住的 November 21st of every year 是同位語，補充說明世界問候日是哪一天；拿掉之後句子結構就很清楚：World Hello Day ______ observed by people in 180 countries. 空格後面是過去分詞 observed 加上 by 帶出的動作者，這是被動語態的標準形狀，所以空格一定是 be 動詞。四個選項都是 be 動詞的變化，真正要決定的只有時態。Since then 指的是從 1973 年一路延續到現在，這種從過去某一點持續到現在的說法，配的是現在完成式（劍橋 English Grammar Today：since 與現在完成式連用）。合起來就是 has been observed（一直被慶祝到今天）。
is：現在式被動，講的是目前的常態，接不上 Since then 所要求的「從某個起點延續至今」。was：過去式，語意變成當時曾經如此、現在不一定，與整篇強調這個節日至今仍在延續的旨意相反。had been：過去完成式，需要另一個更早的過去時間點當參照，本句沒有。
since then（從那時起）、be observed（被慶祝、被遵行）、observe a holiday（慶祝節日）、bring attention to（喚起對…的關注）、be born（誕生、問世）、the conflict between A and B（A 與 B 之間的衝突）。
In the fall of 1973, in an effort to bring attention to the conflict between Egypt and Israel, World Hello Day was born. The objective is to promote peace all over the world, and to 26 barriers between every nationality. Since then, World Hello Day—November 21st of every year— 27 observed by people in 180 countries. Taking part couldn't be 28 . All one has to do is say hello to 10 people on the day.
However, in response to the 29 of this event, the concepts of fostering peace and harmony do not have to be confined to one day a year. We can 30 the spirit going by communicating often and consciously. It is a simple act that anyone can do and it reminds us that communication is more effective than conflict.