英文文法...小學程度..(((10)))))))

I think you should be aware that:

careful is 形容詞
carelessly is 副詞

In addition, they are opposit words.

Careful (形容詞):
1. 仔細的;小心的[(+of/about/with)][+to-v][+v-ing][+Wh-][+(that)]
John was careful not to say anything about this to her.
約翰小心翼翼,避免向她提及此事。
Be careful with the dynamite.
當心這炸藥。
A good writer is careful about details.
凡是優秀作家都重視細節的描寫。
I am always careful when crossing a street.
我過馬路時總是很小心的。
2. 周到的,徹底的,精心的
The doctor gave him a careful examination.
醫生對他作了徹底的檢查。

Careless (形容詞):
1. 粗心的,疏忽的;草率的
He made a careless mistake.
他犯了一個粗枝大葉的錯誤。
2. 隨便的;自然的
He sat into a chair with careless ease.
他隨便往椅子裡舒舒服服一坐。
3. 漫不經心的;淡漠的[(+of/about)]
She's careless about her clothes.
她對穿著一點都不講究。
4. 無憂無慮的
careless days
無憂無慮的日子

Carefully (副詞):
1. 小心謹慎地;警惕地
2. 仔細地;周密地
Now listen carefully everybody.
請大家仔細地聽。

Carelessly (副詞):
1. 粗心大意地,不當心地;漫不經心地
He stuffed the letter carelessly into his pocket.
他隨隨便便地把信往口袋裡一塞。
2. 草率地
3. 淡漠地
4. 無憂無慮地

careful
姐係小心.
e.g.you better careful because that is dangerous.
carelessly
less=without
姐係一個字既反話.
好似useless=無用
careless=唔care

actually, careful and carelessly have two different meanings.

[careful] You have to be careful because its dangerous to walk around here.

[carelessly] Carelessly, I fall down and hurt my ankle.

there isn't any key word that make it clear whether which word should we use. it depends on the meaning of the whole entire senteces.=]