Which is better for "non selected" state?

A) Placeholder

On usability tests, with this options people are omitting this field. They seem to think that it's not required or it's already chosen.

B) Blank

I didn't have usability tests on this yet. The white empty space seems to cause the urgent need to fill it in. What are the actual disadvantages of this?

Other considerations

• There are also other option for placeholder, for example "Select...", "---", "--- Select ---"
• Maybe the text color of placeholder matters? It can't be too dark so that you can see that the field is empty?