Many lessons are now available online, from ______ students can choose for free.

(单选题)Cooper and her colleagues argue that a “town of culture” awa (单选题)The example of Arctic terns in the last paragraph is used ma (单选题)Which of the following is true about animals’ migration? (单选题)Adult salmon swim back to the river because ______. (单选题)According to the passage, monarch butterflies in North Ameri (单选题)（ ） (单选题)（ ） (单选题)（ ） (单选题)（ ） (单选题)Which of the following can be the best title for the text?