“are climbing” is in present progressive tense.
The PRESENT PROGRESSIVE TENSE indicates continuing action, something going on now. This tense is formed with the helping "to be" verb, in the present tense, plus the present participle of the verb (with an -ing ending): "I am buying all my family's Christmas gifts early this year.
The correct answer between all the choices given is the first choice or letter A. I am hoping that this answer has satisfied your query and it will be able to help you in your endeavor, and if you would like, feel free to ask another question.