function. Which of the following is a necessary and sufficient condition for \( x_0 \) to be a global minimizer of \( f \)?</p>
            <ul class="options">
                <li><label><input type="radio" name="q4" value="0"> a) \( \nabla f(x_0) \neq 0 \)</label></li>
                <li><label><input type="radio" name="q4" value="1"> b) \( \nabla f(x_0) = 0 \)</label></li>
                <li><label><input type="radio" name="q4" value="2"> c) \( \nabla^2 f(x_0) \succeq 0 \)</label></li>
                