Nested enumerate in columns

[Paul Smith]

Dear All

Some time ago, Herbert provided here an example for me to achieve the
following enumerate environment in columns:

(a) First item;          (c) Third item;    
(c) Second item;     (d) Fourth item.

Now, I am trying to obtain a nested enumerate environment in columns
as shown bellow:

1. A line of text.
  (a) First item;          (c) Third item;    
  (c) Second item;     (d) Fourth item.
2. Another line of text.

Any ideas?

Thanks in advance,

Paul