Setting a default value in collection_select

Could anybody cast some light on these:

1. How can I set a default value in a collection_select? To be specific, I
have a class 'Platform', and I want to set the platform_code (a field of
Platform) to be 'ORA' (which exists in the Platform table).
I tried many variations of the following code in my view, but in vain:
<% @selected = 'ORA' %>
<%= collection_select "sac_table_platform", "platform_code",
Platform.find(:all, :order => "platform_code"),
:platform_code, :platform_code, { :selected => @selected } %>

2. How can I build my own list of collection_select, e.g., a list of three
people, say, to show [Adam, Bob, Charley] on the collection_select for the
corresponding values ['A', 'B', 'C'] in a table (which already exists), and
use it in my view?