Taking part couldn't be 28 .
答案：(C) easier
【句型】couldn't be easier 固定強調用法「再容易不過了」，比較級表達最高程度的簡單；quicker（更快，通常講難易不是快慢）、sooner（更快，通常指時間）、better（更好，不如 easier 貼切原意「參與很簡單」）都不如 easier 精確。
couldn't be ______ 表面上是否定，很多人第一時間讀成「不可能更…了」，然後把它理解成負面的意思，覺得參與這件事很難。落差就在這裡：這個句型長得像否定，實際上是最高級的肯定。
couldn't be 加比較級的意思是「再…不過了」，也就是已經到達極點。推一次邏輯就通了：既然不可能「更容易」，那就是「已經容易到不能再容易」。你其實背過這個句型最常見的版本：Couldn't be better!（好得不能再好了）。至於要填哪一個比較級，下一句就是答案：All one has to do is say hello to 10 people on the day.（要做的只是在那一天向十個人問好）。這句在說明門檻有多低，講的是難易，不是快慢也不是好壞，所以是 easier。
quicker：更快，談的是速度；下一句說的是只需要做一件小事，重點在簡單而不在快。sooner：更早，指時間的先後，與參與的方式無關。better：更好，語意太籠統；couldn't be better 是在稱讚整體狀況很棒，但這裡要說明的是參與門檻低。
couldn't be better（再好不過了）、couldn't agree more（再同意不過了）、couldn't care less（一點也不在乎）、take part in（參與）、all you have to do is（你要做的只是…）、say hello to（向…問好）。其中 take part in 這一組考過 6 個年度，83 年第 26 題 →、85 年第 23 題 →、98 年第 28 題 →、106 年第 29 題 →、107 年第 18 題 →都出現過。
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.