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to expand; to swell (out); to get big; to become inflated
酵母を入れるとパン生地が膨らんでいくよ。
When you add yeast, the bread dough rises.
オーブンの中でパン生地がきれいに膨らんだ。
The bread dough expanded nicely in the oven.
春になって木のつぼみが膨らんでいる。
The tree buds are swelling now that spring has come.