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From: cdsm@icdoc.UUCP (Chris Moss)
Newsgroups: net.singles,net.nlang
Subject: Re: Grammar and Spelling on the Net
Message-ID: <293@ivax.icdoc.UUCP>
Date: Mon, 3-Mar-86 08:58:55 EST
Article-I.D.: ivax.293
Posted: Mon Mar  3 08:58:55 1986
Date-Received: Sun, 16-Mar-86 00:32:05 EST
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Reply-To: cdsm@icdoc.UUCP (Chris Moss)
Organization: Dept. of Computing, Imperial College, London, UK.
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>
>Wrong.  The marked words are plaural pronouns.  In each sentence, the
>subject is singualar.  The correct pronoun is "his," although some would
>argue for "his/her."
>
>Jeff Siegal - MIT EECS

Consult the Oxford English Dictionary for a more authoritative angle on this.
It quotes singular uses of 'their' and even 'they' dating back to the
sixteenth or seventeenth century (I think), and accepts the usage. 
If you want to argue right against wrong, use authorities worthy of the name!

I won't comment on Jeff's spelling :-)

Chris Moss, Imperial College, London.