Because lesquels replaces the noun, while quels goes directly before a noun.
Compare:
So:
You would not say lesquels outils.
It agrees with the noun it refers to: outils.
Outil is masculine, and outils is plural, so the matching form is lesquels.
The full set is:
Even though English just says which one / which ones, French shows gender and number.
Ces means these or those, depending on context.
It is the plural form of the French demonstrative adjective:
In this sentence, ces outils means these tools.
French does not always sharply separate this/these from that/those the way English does; context usually makes it clear.
Because this sentence uses inversion, a common way to form a direct question in standard French.
Statement:
Question with inversion:
In inversion, the verb and subject pronoun switch places and are joined by a hyphen:
This structure is common in:
In everyday speech, people often prefer:
It is the present tense of garder.
Here it usually means something like:
The French present can cover meanings that English expresses with the simple present, and sometimes also with other present-time phrasing depending on context.
In this sentence, the most natural English translation is the simple present: do you keep.
Dans means in or inside.
So:
That is the natural preposition because the tools are located inside the drawer.
Yes, but it sounds a bit more standard or formal because of the inversion gardes-tu and the use of lesquels.
A more conversational version would often be:
Or:
All three are correct, but they differ in style:
The final -s of gardes is normally silent.
So gardes-tu is pronounced roughly like gard tu.
Important points:
So the spelling changes for grammar, but the pronunciation stays simple.