The case for STPM 2007 is you are allowed to answer the science paper in either BM or English.
However, you are not allowed to answer using both languages alternately.
Hence, only one language , BM or English.

Hmm... all I can say is... To take part in the Science Olympiads is not easy in Malaysia.
You have to go through several selection processes.
The fact that these selection processes are not known to many just increased the difficulty.
So far till 2006 (Malaysia is still a new participant in the olympiads), the selection is not open.
The education department of each state will select certain schools and the selected schools will then choose a few representatives.
These representatives will go through strings of tests (hmm...imagine lab rats ) before finally selected to represent Malaysia.

This is how it is done here. I am not sure about other countries though.

Please correct me if I am wrong.