=1

你

nǐ

you (informal, as opposed to courteous 您 nín)

=1

你

nǐ

you (Note: In Taiwan, 妳 is used to address females, but in mainland China, it is not commonly used. Instead, 你 is used to address both males and females.)

2

在

zài

to exist; to be alive (of sb or sth) to be (located) at (used before a verb to indicate an action in progress)

3

写信

xiěxìn

to write a letter

=4

吗

má

(coll.) what?

=4

吗

mǎ

used in 嗎啡 mǎfēi

=4

吗

ma

(question particle for "yes-no" questions)