Dropping the indefinite article.

Hi.
My German is largely self taught so, although it seems to work OK(ish) in Germany, I know that the grammar is a mess. I have bought Rocket German to try and add some structure. So far I have been knocking through the Beginners course at a fair rate but I am now starting to encounter things that I don't properly understand. 
In 5.5 the expression 'Sie fährt Motorrad.’ is used with the translation 'She drives a motorbike.' I expected it to read 'Sie fährt ein Motorrad.’ Same thing also happens with ‘Auto’.
Can somebody please explain why there is no indefinite article. I know that there is no indefinite article with plurals but I don’t think that Motorrad is plural.
Regards Fred

Hi Fred,

'Sie fährt Motorrad' and 'Sie fährt ein Motorrad' are both correct. It is okay to leave out the article in German for singular. In English you can't translate it to 'she drives motorbike'. It only works for plural in English to leave out the article 'she drives motorbikes'. 

Regards

Paul