1. aloud
可作副词，意思为“出声地”或“大声地”。aloud作“出声地”含义时，主要与read, think等连用，表示声音可以被听到。作“大声地”含义时，主要与shout, call, cry等词连用。例如：
He read her letter aloud to the rest of the family.
他把她的信大声读给家人听。
The little boy is crying aloud.
那个小男孩哭的很厉害。
2. loud
作副词讲：意为“响亮地”、“大声”或“高声地”，指音量大，传播距离较远。一般多用来修饰 speak ， talk ， laugh 等动词，主要指说话声、笑声和爆炸声等等。常用比较级形式。
Try to sing louder.
试着再大点儿声唱。
Could you speak a little louder, please?
请你说话大声一点，好吗？
I heard a loud bang and then saw black smoke.
我听到砰的一声巨响，接着就看到了黑烟。
另外，loud作形容词讲：意为“大声的；响亮的”
I couldn't hear what he said because the music was so loud.
我听不见他说些什么，因为音乐的声音太大了。
I heard a loud crash in the kitchen.
我听到厨房有一声巨响。
3. loudly
副词，意为“响亮地、大声的”，既可与发音器官连用，还可以与 ring ，knock 等动词连用。loudly 放在动词前后均可，含有“喧闹”或者“嘈杂”的含义。
Someone knocked loudly at the door.
有人大声敲门。
She spoke very loudly.
她说话的声音很大。
Don't talk so loudly.
别这么高声说话。
小练习：
Someone burped ____ at the back of the hall.
Loudly aloud loud
Too ____sound would strain your ears.
Loudly aloud loud
The teacher read the poem____ to the pupils.
Loudly aloud loud
答案：loudly；loud ；aloud
