Grammatically correct<br/><ol><br/><li>I am working <b>for </b>or<b> in </b>the administration.</li><br/><li>We <b>go </b>or <b>are going </b>to the meeting.</li><br/><li>There must <b>be no</b> or <b>not be any</b> mistakes in a business letter.</li><br/><li>Mr. X is 80 years old and you are surprised. Do you write I thought he <b>is </b>or <b>was </b>younger.</li></ol>