Choose A, B, C, or D for the correct answer.

The following text is for questions 10 to 13.

    We should wear masks when we are outside in order not to be infected by coronavirus. We'd better wear masks made of cloth and wash them daily. Well, let me tell you how to wash a mask cleanly.

    We need detergent, water, a bucket, hanger, and clip. Now, pour water into the bucket sufficiently. Then, add enough detergent into the bucket. After that, put in our dirty mask and soak for 10 to 15 minutes. Make sure all parts of the mask are immersed in the water.

    After 10 to 15 minutes, cleanse the mask. Make sure that your hands remain clean. Take the mask and wash it gently. Cleanse the mask using flowing water. Make sure that it is free from detergent. Then, dry it with a hanger and clip under the hot sun. Please remember, iron the mask before using.

"After that, put in our dirty mask and soak for 10 to 15 minutes." (Paragraph 2)

What does the underlined word mean?