Breakdown of Luuletko, että se on jyrkin rinne?
olla
to be
se
it / he / she (of a person) / that
että
that (conjunction)
luulla
to think, to suppose
Questions & Answers about Luuletko, että se on jyrkin rinne?
What is the base form of jyrkin (steepest), and why does it only have one k?
The base adjective is jyrkkä (steep). To make the superlative form for "steepest", we add the suffix -in. Adding this suffix closes the syllable, which triggers consonant gradation. The strong double kk weakens to a single k, and the final vowel ä drops out to make room for the -in, giving us jyrkin.
Could I say Ajatteletko, että... instead of Luuletko, että...?
It is much more natural to use luuletko here. In Finnish, luulla means "to think" in the sense of assuming, supposing, or having an opinion. Ajatella means "to think" in the sense of actively pondering or processing thoughts. Since you are asking for an opinion or assumption about the slope, luulla is the correct choice.
Why is there a comma before että? We usually don't put one before "that" in English.
Finnish punctuation rules are strict about this! You must put a comma before että (that) because it introduces a subordinate clause. Whenever a sentence is split into a main phrase (Luuletko) and a secondary phrase with its own subject and verb (se on), Finnish separates them with a comma.
Why are jyrkin and rinne in the basic nominative form instead of the partitive?