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diff --git a/1000-hours/public/images/speech-tract-r.dark.svg b/1000-hours/public/images/speech-tract-r.dark.svg
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diff --git a/1000-hours/public/images/speech-tract-tdsz.dark.svg b/1000-hours/public/images/speech-tract-tdsz.dark.svg
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diff --git a/1000-hours/public/images/speech-tract-θð.dark.svg b/1000-hours/public/images/speech-tract-θð.dark.svg
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diff --git a/1000-hours/sounds-of-english/16-tdsz.md b/1000-hours/sounds-of-english/16-tdsz.md
index 53c2662c..00de0553 100644
--- a/1000-hours/sounds-of-english/16-tdsz.md
+++ b/1000-hours/sounds-of-english/16-tdsz.md
@@ -4,7 +4,7 @@
`t, d, s, z` 这 4 个辅音的发声关键,在于它们发声时起始的**舌尖位置**。
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+
在中文普通话里,`t, d` 这两个声母发声时起始的**舌尖位置** 贴在牙齿上;`s, z` 这两个声母发声时起始的 “舌尖位置” 接近牙齿,但留了个空隙以便气流通过。你可以试着用中文普通话说一遍 “我踢死你”(`wǒ tī sǐ nǐ`)。
diff --git a/1000-hours/sounds-of-english/21-θð.md b/1000-hours/sounds-of-english/21-θð.md
index 9dfcb975..8699f48e 100644
--- a/1000-hours/sounds-of-english/21-θð.md
+++ b/1000-hours/sounds-of-english/21-θð.md
@@ -2,7 +2,7 @@
`θ, ð` 这两个辅音,学校里常见教材一般都强调说**一定要把舌尖夹在齿间**再开始发音。其实不一定要那么严格,实际上,舌尖即便没有伸出到齿外也可以,大多数时候,只要舌尖贴到上齿之后开始发音就可以了。
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diff --git a/1000-hours/sounds-of-english/22-r.md b/1000-hours/sounds-of-english/22-r.md
index ce46922c..82c05866 100644
--- a/1000-hours/sounds-of-english/22-r.md
+++ b/1000-hours/sounds-of-english/22-r.md
@@ -2,7 +2,7 @@
`r` 这个辅音原本不难,但,美式英语有个独特之处造成了困难。它的难度并不在于发音起始的 “舌尖位置”,而是 “舌尖姿势”。英式英语中,`r` 只有一种 “舌尖姿势”,舌尖向前贴在上颚;可在美式英语中,*rock* `r/ɔk/` 是舌尖向前的,但,*card* `/kɑːʳd/` 的舌尖姿势却是后卷的。
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diff --git a/1000-hours/sounds-of-english/23-l.md b/1000-hours/sounds-of-english/23-l.md
index 6c4a909c..2ee075b1 100644
--- a/1000-hours/sounds-of-english/23-l.md
+++ b/1000-hours/sounds-of-english/23-l.md
@@ -10,6 +10,4 @@
所以,要格外注意 `l` 在元音之后的情况,注意舌尖位置正确,动作完整,不能有嘴唇动作 —— 否则就会出现 `ʊ` 音。
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