Ex.<br/><br/>a. The most used technology in the US is the smart phone.<br/><br/>b. .... is a smart phone.<br/><br/>c. .... are smart phones.<br/><br/>d. ..... is smart phone.<br/><br/>Q. Are the above all grammatically correct and academically acceptable? <br/><br/>Can all of the above be started as the starting sentence?<br/><br/>Thanks in advance.