What is most likely to cause mutation

Change in a DNA sequence

Explanation:

Copying, exposure to ions etc

✿   this landform has a high elevation and a high relief

✿   this landform is a mountain

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products