Il y avait je ne sais quoi dans son caractère qui me déplaisait,
Je ne sais à quoi vous pensez,
There was something in his character which displeased me.
I know not of what you think.

9. Dont, whose, of whom, of which, used for persons and things, is invariable.

Je parle des parents dont l'enfant s'est noyé hier,
Ce dont vous parliez hier est arrivé,
I speak of the parents whose child was drowned yesterday.
Of what you spoke yesterday has happened.

10. De qui is preferable to dont whenever in English we would rather say from which than of which.

Le floriste de qui j'ai reçu ces fleurs,
The florist from whom I have received these flowers.

11. Lequel, laquelle, lesquelles, who, which one, relate to persons and things, and should stand only for nominatives and objectives, to avoid ambiguity.

Voilà deux vases, lequel voulez-vous?
Laquelle de vos filles est l'ainée?
L'esclave était la propriété du maître, au pouvoir duquel rien ne pouvait le soustraire,
L'homme à qui or auquel je me suis adressé,
Les femmes pour qui or pour lesquelles vous faites des emplettes,
Here are two vases; which one will you have?
Which one of your daughters is the eldest?
The slave was the master's property, from the power of whom nothing could extricate him.
The man to whom I have applied.
The women for whom you make some purchases.

12. En, of it, of them, is invariable, and relates mostly to animals and things.

Vous en parlez, you speak of it.
J'en ai, I have some of it.

(See en joined to the verb avoir, in § 33.)