An army of white pelicans was drawn up in a row across the middle of the creek, the water reaching half-way up their bodies, while they stood upright with their necks raised in the air, evidently engaged in some important occupation, in which they were so absorbed that they did not observe our approach. (In the Wilds of Florida 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。
An army of white pelicans was drawn up／（前置詞の前）in a row across the middle of the creek,／（コンマの後）the water reaching half-way up their bodies,／（接続詞の前）while they stood upright／（前置詞の前）with their necks raised in the air,／（コンマの後）evidently engaged in some important occupation,／（前置詞の前）in which they were so absorbed that they did not observe our approach.
語句のかたまりを前から訳していきます。
An army of white pelicans was drawn up
白いペリカンの一団が整列していた
in a row across the middle of the creek,
入江の中央を横切るような形で一列になって
the water reaching half-way up their bodies,
体の半分まで水につかって
while they stood upright
その間、彼らは直立していた
with their necks raised in the air,
首をまっすぐ上に伸ばして
evidently engaged in some important occupation,
何か大事な作業を行っているようだった
in which they were so absorbed that they did not observe our approach.
彼らはあまりに作業に集中していたので、私たちが近くにいることに気づかなかった
An army of white pelicans was drawn up in a row across the middle of the creek, the water reaching half-way up their bodies, while they stood upright with their necks raised in the air, evidently engaged in some important occupation, in which they were so absorbed that they did not observe our approach.
was drawn up in a row→ was drawn up = 整列していた、in a row = 一列で
with their necks raised in the air→ 付帯状況のwithです。with●▲ = ●を▲の状態にして。● = their necks、▲ = raised in the air
白いペリカンの一団が、入江の中央を横切るような形で一列になり、体の半分まで水につかって整列していた。彼らは首をまっすぐ上に伸ばして直立し、何か大事な作業を行っているようだった。彼らはあまりに作業に集中していたので、私たちが近くにいることに気づかなかった。
An army of white pelicans was drawn up in a row across the middle of the creek, the water reaching half-way up their bodies, while they stood upright with their necks raised in the air, evidently engaged in some important occupation, in which they were so absorbed that they did not observe our approach.
今回の課題文の「骨格」（中心部分）は An army of white pelicans was drawn up in a row across the middle of the creek で、残りの部分はそれと同時に起きていることの描写になっています。
the water reaching half-way up their bodies→ 独立分詞構文で付帯状況を描写。
while they stood upright with their necks raised in the airy→ 接続詞while を使って、同時に起きていることを描写。
evidently engaged in some important occupation→ 分詞構文で付帯状況を描写。
in which they were so absorbed that they did not observe our approach→ 関係代名詞を使って補足説明。先行詞は some important occupation です。
