Question

ゆ

三行目のwhenは関係副詞ですか？

However, many difficulties to reaching the cleaner energy future
imagined in the Paris conference remain. One is technological. Batteries
capable of storing energy for use when the sun is not shining and the
wind is not blowing are still quite expensive, though their costs are
falling.

Answer 1

✨ ベストアンサー ✨

めい

接続詞「～時」です😊