他给我寄了一___信。
He sent me a letter. Which measure word?
全球翻车率（内测预估）
A个
gè · generic measure word
B张
zhāng · measure word for flat sheets
✓封
fēng · measure word for letters
D条
tiáo · measure word for long thin things
信用“封”，因为要封口。中文量词偶尔也是讲道理的。
封 (fēng, “to seal”) counts letters — one of the rare measure words with visible logic.