Form an adjective from the words in brackets by adding -ed or -ing. It's so ___ (frustrate)! No matter how much I study I can't seem to remember this vocabulary.

The correct answer is frustrating. Explanation: * When we describe something that causes frustration, we use the -ing form of the adjective. In this case, the difficulty of memorizing vocabulary causes frustration. Therefore, 'frustrating' is the suitable adjective to describe the situation. * The -ed form, 'frustrated', would be used to describe how someone feels. For example, 'I am frustrated because I can't remember this vocabulary.'