the cost of mobile phones单数还是复数?

the cost of mobile phones单数还是复数? 英语翻译The plane retired after thousands of hours’flying.It was bought for less than $2000 by the school,half the cost of a mobile classroom. the cost of the cost of pat the kind of mobile phones 主语是 The advantage or disadvantage of mobile phones? at the cost of意思 THE COST OF LIVING怎么样 THE COST OF LIVING怎么样 the cost of的意思 是COVER THE COST OF 还是MEET THE COST OFXIEXIE How much does the mobile phone ____?填cost还是spend还是pay还是take? what's the function of a mobile phonewhat can people do with a mobile phone? total+cost+of+the+trip是什么意思 Build the bridge cost lots of money money covers the cost of sth 翻译 the high cost of materials是什么意思 the opportunity cost of capital是什么