After this we walked on for a mile, and had begun to wonder what had become of our companions, and to be a little anxious at having missed them, when we were startled at hearing a loud roar not three hundred yards from us. (A Voyage round the World by W.H.G. Kingston）
動画の後半部分でリスニング用音声が流れます。
英文を前から読んでいくために、語句のかたまりを作ります。こんな具合に課題文をスラッシュ（斜め線）で区切ります（スラッシュリーディング）。語句のかたまりを意識すると、リスニングで英語の意味をつかむのが楽になります。
After this／（主語が文頭にないときの主語の前）we walked on for a mile,／（接続詞の前）and had begun to wonder／（疑問詞の前）what had become of our companions,／（接続詞の前）and to be a little anxious at having missed them,／（接続詞の前）when we were startled／（前置詞の前）at hearing a loud roar not three hundred yards from us.
語句のかたまりを前から訳していきます。
After this
この後
we walked on for a mile,
私たちは１マイル歩いた
and had begun to wonder
そして、〜と思いはじめた
what had become of our companions,
私たちの仲間はどうなったのか
and to be a little anxious at having missed them,
そして、彼らとはぐれてしまったのではないかと少し心配になり（はじめた）
when we were startled
そのとき、私たちはびっくりした
at hearing a loud roar not three hundred yards from us.
私たちから300ヤードも離れていない所で大きな吠え声が聞こえて
After this we walked on for a mile, and had begun to wonder what had become of our companions, and to be a little anxious at having missed them, when we were startled at hearing a loud roar not three hundred yards from us.
what had become of our companions→ what becomes of ●? = ●はどうなるか
we were startled at hearing a loud roar→ be startled at 〜 = 〜に驚く
この後、私たちは１マイル歩き、私たちの仲間はどうしたのかと思いはじめ、彼らとはぐれてしまったのではないかと少し心配になりだしたとき、300ヤードも離れていない所で大きな吠え声が聞こえて、びっくりした。
今回の課題文には、ペアになっている不定詞があります。ペアになっていることを見逃すと、後ろの不定詞の意味がとれなくなるので気をつけましょう。
（we）had begun to wonder what had become of our companions, and to be a little anxious at having missed them
to wonder what had become of our companions
（we）had begun＜ and
to be a little anxious at having missed them
