Sed help: string match

Sed help: string match

I have a few systems I where I need to modify the /etc/fstab. The fstab
contains
/var /var ext3 default,nodev,nosuid 1 2
/var/log /var/log ext3 default,nodev,nosuid 1 2
/var/log/audit /var/log/audit ext3 default,nodev,nosuid 1 2
I need to modify the /var entry removing the nodev mount option. I'd like
to use sed but cant' figure out how to modify that exact line. Everything
I've tried modifies all lines containing /var.
Would appreciate any help as I keep banging my head against the wall.
Thanks, Bert