What type of crowd is commonly seen during picket lines?

The correct choice is expressive, as picket lines are often formed as a means of communication and demonstration by individuals or groups seeking to convey their grievances or demands. This type of crowd is characterized by a strong sense of purpose and emotion, as they aim to express their views on a particular issue, often related to labor disputes, social justice, or political matters.

In this context, demonstrators typically group together to showcase solidarity, using chants, signs, and other forms of visual communication to articulate their message and garner support from the public. The primary goal is to communicate a specific message rather than engage in confrontation or disorder, which aligns with the expressive nature of crowds seen at picket lines.