_______ in thought, he almost ran into the car in front of him.
C
这里分词短语的意义应为“Ashewaslostinthought”，意为“由于陷入沉思”，这儿填入过去分词短语，表示一种状态，用作原因状语。
Touristexpenditureshavedifferenteffectsonadestinationeconomy:salesbyfoodvendorstorestaurantsare_______effect;whiletaxifaresandairlineticketsalesare_______effect.
InEurope_______arethetwoleadingcontendersforaglobalreservationssystem.
Scientistsdoubtwhetherit’s________toregulateone’sbiologicalclockbydrinking.