地: from adjective to adverb (认真地学习)
【一20】【一28】结构助词“地” / 状语
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
Adjective / Adverb + 地 + Verb
地 (de, pronounced just like 的!) turns an adjective into a manner adverb, like English “-ly”: 认真 (serious) → 认真地学习 (study seriously).
他高兴地说：“我明天回家！” (he said happily: …)
“Adj. + 地” goes before the verb.
One-syllable adjectives often skip it: 快走！ (walk fast!), 慢点儿 (slow down). In short commands 地 is often dropped: 你认真写！
Memo: 的 + noun (我的书), 地 + verb (认真地写).
Examples
他高兴地说：“我明天回家。”
Tā gāoxìng de shuō: “Wǒ míngtiān huí jiā.”He said happily: “I'm going home tomorrow.”
我们要认真地准备考试。
Wǒmen yào rènzhēn de zhǔnbèi kǎoshì.We need to prepare for the exam seriously.
你认真写！
Nǐ rènzhēn xiě!Write carefully!
孩子们高兴地唱歌。
Háizimen gāoxìng de chàng gē.The children sing happily.
Common mistakes
✗ 他说高兴地 (from “he said happily”) → ✓ 他高兴地说.
✗ 认真的学习 (in standard writing) → ✓ 认真地学习 (的 before nouns, 地 before verbs).