He was so deep in thought, thinking of the problem ________he knocked into the tree without noticing it.
31.-----She missed her train to London,____she didn"t seem to care. ---- Well, there is anotherl one in 15 minutes.
30.Mr.Snuth advised us to________a written agreement even it was just a small deal.
29.There are also instructions about the________of all the buttons and switches.
28.The university with two____campuses hasa student population of 50,000 in total.
27.Let' s move all the products into the hall and_____them in a proper order.