Which of the following aquatic plants are commonly targeted by herbicides?

Water hyacinth and duckweed are commonly targeted by herbicides due to their rapid growth and ability to form dense mats on the surface of water bodies, which can significantly hinder aquatic ecosystems. These plants can lead to problems such as reduced light penetration, oxygen depletion, and disruption of fish populations, making them a priority for control measures.

The use of herbicides on these species is typically because they can outcompete native aquatic vegetation for resources, effectively altering habitats and decreasing biodiversity. Herbicides are effective in managing their spread, and regulatory guidelines often focus on these specific plants because of their invasiveness and the ecological threats they pose.

In contrast, while cattails, bulrushes, lotus, lily pads, salvinia, and marsh grass can also be found in aquatic environments, they are often not the primary targets of herbicides in many management scenarios. This is due to various factors, including their ecological roles in providing habitat for wildlife or being less aggressive than the species identified in the correct answer. Therefore, the focus on water hyacinth and duckweed makes option B the right choice.