How did you come up with this crazy idea?

I had a good idea.

I hit upon a good idea.

I got it into my head to go there by myself.

I hit on a good idea.

Taken by surprise, I couldn't think of anything to say.

She came up with a possible solution.

She hit upon a good idea.

She couldn't think what to give the children for Christmas.

She came up with a good way of making money by using the Internet.

A good idea struck her.

She thought of a good plan.

She thought of a good solution.

It never occurred to me that she was ill in hospital.

They conceived a plan to surprise the enemy.

He has hit upon a good idea.

He hit on the plan after long meditation.

He hit on the answer to the problem as he was having lunch.

He thought up a new idea.

He thought of a good idea.