as shown in the code posted below, i want to add a drop down list. but visual studio code underscored the v-for in red and generates the following error:

Elements in iteration expect to have 'v-bind:key' directives

what does that mean and how to fix it please?

code:

<select name="" id="" v-model="selected">
    <option value="" disabled>Select a car</option>
    <option v-for="car in cars">{{ car }}</option>
  </select>