Question

movement of rivers and oceans
the constant flow of water transforms the surrounding environment.
landslide
a landslide encompasses a broad spectrum of soil movements.
crystallization
during the cooling process of magma, crystallization begins as a consequence of the decrease in temperature.
different geological processes act at different rates, ranging from extremely fast acting on fractions of seconds to minutes to days, to very slow acting over millions to billions of years.
click on the card that represents a slowest process.

Explanation:

Step1: Analyze movement of rivers and oceans

The movement of rivers and oceans is a continuous but relatively fast - changing process in geological time - scales, but not the slowest.

Step2: Analyze landslides

Landslides are sudden events that can occur in a short time, from seconds to minutes in most cases.

Step3: Analyze crystallization during magma cooling

The cooling of magma and subsequent crystallization is a very slow process that can take thousands to millions of years as magma cools deep within the Earth's crust or mantle.

Answer:

Crystallization