Hello, I am Yoshi from NILS Japanese language school.
N1 [の中（なか）で]　何／どこ／だれ／いつ　が　いちばん　adjectiveですか
—N2が　いちばん　adjectiveです
This question pattern is used to ak the listener to choose something that is the most “adjective.” Thi choice is made from the group or category denoted by N1. The interrogative used is decided by the kind of category from which the choice is made.

(Example)
日本料理（にほんりょうり）[の　中]で　何が　いちばん　おいしいいですか。
—てんぷらが　いちばん　おいしいです。
Among Japanese dishes, what is the most delicious?　　—Tempura is.

ヨーロッパで　どこが　いちばん　よかったですか。
—スイスが　いちばん　よかったです。
In Europe, where did you like best?　　—I liked Switzerland best.

家族（かぞく）で　だれが　いちばん　背（せ）が　高いですか。
—弟（おとうと）が　いちばん　背が　高いです。
Who is the tallest of your family?　　—My younger brother is.
*家族：　family
*背が高い：　tall

1年で　いつが　いちばん　寒（さむ）いですか。
—2月が　いちばん　寒いです。
When is the coldest time of a year?　　—It’s the coldest in February.

Note that the article が is used when the subject is an interrogative. See Lesson 10-(2).
When the subjet of an adjective sentence is questioned, the particle が is attached to the interrogative in the same way.

August 21st News, from NILS Japanese language school.