The correct version is there are many threats to dolphins' continued existence, and humans are just one.
I think it is A. was waving at the flag. This is just my opinion is I may be wrong. Please feel free to correct me in the comments. Have a nice day!
Answer:
"What (did) you (do) there? Come to me!" our teacher (shouts or shouted). We (found) a nice place for a picnic. But nobody (ate) a banana, but the gorillas (had) a nice lunch that day. It (was) a great day at the zoo, and we (had) a lot of fun.
B because it is dangerous
