英语中部分动词的过去式或过去分词以后缀 “-ed” 结尾。在这些动词中，后缀 “-ed” 有三种发音方式。分别是哪三种？应如何判断？
 
Did you know these two letters can be pronounced in three different ways? 
They can be /d/, /t/ or /?d/. Here's how to find out which.
First, feel your neck. If a sound makes it vibrate like /d/, then it's voiced. If it doesn't like /t/, then it isn't.
Where 'ed' comes after a vowel or a voiced consonant, then pronounce it as /d/, which is a voiced sound. Played, used.
If you have 'ed' after an unvoiced sound, then it sounds like /t/ – an unvoiced sound. Looked, helped.
If you have 't' or 'd', then 'ed' becomes /?d/ – it's just easier to say. Wanted, needed.
So, if 'ed' comes after a voiced sound, then it's voiced. If it comes after an unvoiced sound, then it's unvoiced, and if it comes after /t/ or /d/, then it's /?d/.
 
用法总结
 
1. 动词以元音或浊辅音结尾时，后缀 “-ed” 读作 /d/。
played
used
paved
slowed
 
2. 动词以清音结尾时，后缀 “-ed” 读作 /t/。
looked
helped
fixed
cracked
 
3. 动词以 /t/ 或 /d/ 结尾时，后缀 “-ed” 读作 /?d/。
wanted
needed
printed
moulded