Peter scanned the yellow pages looking for the number of a plumber. 為什麼scan後面的動詞look是用looking ?

Peter scanned the yellow pages looking for the number of a plumber. (O)
and
Peter scanned the yellow pages to look for the number of a plumber. (O)
都是可行的寫法．
主要動詞是scanned．looking for 或是to look for都是用來表示＂目的＂．


The boy's indifference to schoolwork （主詞）worried　（動詞） his parents（受詞）.
這裡的worried前有省略字嗎?
沒有，這句子本身就是一個完整的句子．
他的意思是：

男孩子本身對功課的無謂讓他的父母擔心了．

Other popular ways to say the same thing are:
1. ... made his parents worried.
2. ... had his parents worried.

Actually, "looking" is redundant in the sentence.
"scan something for something" is already an idiomatic expression bearing the meaning of looking for something.

Peter scanned the yellow pages for the number of a plumber. (a sentence more concise)

"worry" can be used as a transitive verb with meaning "to make somebody feel anxious about something"

The sentence is correct in grammar and it can also be written as:
What worried his parents was the boy's indifference to schoolwork.

(or, It worried his parents that the boy was indifferent to schoolwork.)

Peter scanned the yellow pages,looking for the number of a plumber.此句在pages後應加一逗號，其後looking ——————為分詞片語當副詞修飾前主要子句。
worried為及物動詞，令其雙親苦腦，所以全句完整無誤