III:
Mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the following questions.
Trả lời câu hỏi dưới đây:
The behavior of many volcanoes ______ very difficult to predict, especially the more explosive types.
Đáp án là B. Chủ ngữ là “The behavior of …” số ít => dùng “is”