绕口令“四是四，十是十，十四是十四，四十是四十”练的是？
The classic “4 is 4, 10 is 10…” tongue twister trains which distinction?
全球翻车率（内测预估）
✓s 和 sh 的发音区分
s hé sh de fā yīn qū fēn · telling s and sh apart
B数学口算
shù xué kǒu suàn · mental arithmetic
C前后鼻音
qián hòu bí yīn · front and back nasal endings
Dl 和 n 的区分
l hé n de qū fēn · telling l and n apart
sì shí shísì sìshí——说不清的，罚抄十四遍，或者四十遍。
It drills s vs sh (sì=4, shí=10). Southern Chinese speakers famously struggle too — you're in good company.