4 sentences

1. 他经常参加各种公益活动。

   tā jīng​cháng cān​jiā gè zhǒng gōng​yì huó​dòng.

   He frequently participates in various public welfare activities.

   Source: Dong Chinese Dictionary

2. 他非常热衷于各种公益活动。

   tā fēi​cháng rè​zhōng yú gè zhǒng gōng​yì huó​dòng.

   He is very enthusiastic about various public welfare activities.

   Source: Dong Chinese Dictionary

3. 社会各界人士都积极参与了这项公益活动。

   shè​huì gè​jiè rén shì dōu jī​jí cān​yù le zhè xiàng gōng​yì huó​dòng.

   People from all walks of life actively participated in this public welfare activity.

   Source: Dong Chinese Dictionary

4. 这几个年轻人发起了一项保护海洋环境的公益活动。

   zhè jǐ gè nián​qīng​rén fā​qǐ le yī xiàng bǎo​hù hǎi​yáng huán​jìng de gōng​yì huó​dòng.

   These young people initiated a public welfare campaign to protect the marine environment.

   Source: Dong Chinese Dictionary