Another clue, earlier in the story:

Quote
"So does this mean you'll marry me?"

That woke her up. "Clark, you can't ask me that here, now."

"Why not? Lois..."

"Why not? Clark! What will we tell our kids? You know when they
ask that question that all kids ask, like the one I asked your parents last
night." She quoted her question, "How did Jonathan propose, Martha?" She
continued, "Only our kids are going to be little the first time they ask
it. What are you going to say to them, Clark? "Oh, we were lying stark
naked in the woods after we'd had sex and I popped the question." I don't
think so."

Clark laughed, "So that means yes?"

"Clark," her voice was a warning as she got to her feet. "Don't
you dare..." She stopped, looking around at the bits of clothing that were
strewn in a small circle around them, and then fished out a couple of lacy
scraps. Clark rose to his feet beside her, kissed her lightly, and then
reached over to pick up her shirt.

His eyes were teasing and happy as he helped her on with the shirt,
carefully buttoning it up for her as he spoke. "Okay, I'll do it properly,
later, when we're both fully dressed. Maybe I'll go down on bended knee.
I'll have to think about this, plan it just right," he gestured with his
right hand, sketching an imaginary setting where all this would happen.

Lois looked at him, standing in that small circle of sun in the
woods, the light caressing the muscles of his powerful body as he happily
sketched out what he thought would be a good proposal for children to hear.
He was the most amazing man, she thought. She handed him his shirt.
"Here, cowboy. Put on your shirt and take me to Shuster's field."
Simona smile