Read the following annoucement and mark the letter A, B, C, or D on your answer sheet to indicate the option that best fits each of the numbered blanks

COMMUNITY CLEAN-UP DAY
Our school is organizing a Community Clean-up Day to raise students’ awareness of protecting the environment. The activity will be held at the central park this Sunday morning, and all students are encouraged to take part.
Last year, while volunteers (11) __________ the park, many local residents came to help with useful tools. The event has continued to grow and attract more participants each year.
Students are encouraged to participate by (12) __________ rubbish and planting trees together. This activity provides a great chance for students to develop teamwork skills and social responsibility.
By joining the event, students can make a (13) __________ contribution (đóng góp) to the environment and feel proud of their actions. Such activities are very (14) __________ in building a better community.