We take this opportunity to express our sincere         of your timely help.

As more and more cars are produced and used, so the _____ from their exhaust-pipes contains an even larger volume of poisonous gas.

Don’t leave matches or cigarettes on the table within      of little children. 

At the class meeting the students discussed three different _______ to the study of English.

Walking down the street, she noticed a long _____ of houses, all exactly alike.