The Availability of Nutrient Cations Such as Ca²⁺, K⁺, and Mg²⁺

The availability of nutrient cations such as Ca²⁺, K⁺, and Mg²⁺ to plants may be insufficient in some soils that have low amounts of _______ particles. These particles have _______ that allow them to hold onto cations and exchange them with the soil solution.

A) sand; strong positive charges
B) clay; weak negative charges
C) sand; semicrystalline structures
D) clay; irregular structures