but it is a language/grammar question really. The toothpaste advert where the girl says "I had no idea that some of the foods I had been eating can cause acid wear" - shouldn't that be 'could cause acid wear'?
Not a good turn of phrase, 'acid wear' sounds wrong anyway, a lazy way of saying ...."some of the foods I have been eating causes acid which wears the enamel from my teeth".
I suppose the conditional 'could' suggests an 'if'; the foods could cause acid wear only if certain conditions were met. The advertiser doesn't want to openly admit of that possibility but wants to suggest that some of the foods definitely cause acid wear in some people and so they ' can' cause acid wear.
Sorry, only kidding, I think you are quite correct in bringing this grammar error to AB readers' attention.
There's lots of other things that annoy me in English writing that I read, particularly in site forums, though I'll save thatrelated topic for another day. :)