Answer:
The correct sentence is:
b) Please remember to buy me those concert tickets.
This sentence is grammatically correct and makes sense. The other sentences contain various grammatical errors:
a) "I remember hear this song the first time we met" should be "I remember hearing this song the first time we met."
c) "Try plug the headphones in!" should be "Try plugging the headphones in!"
d) "I tried to hearing all the words in the song" should be "I tried to hear all the words in the song."
Regarding the second set of sentences, the correct sentence is:
c) Today, parents believe it's too risky.
This sentence is grammatically correct and makes sense. The other sentences contain various grammatical errors:
a) "I must go to school by myself when I was little" should be "I had to go to school by myself when I was little."
b) "I was allowed to play in the streets" is grammatically correct, but it is in past tense, while the other sentences are in present tense.
d) "They don't let children to go alone in the night" should be "They don't let children go alone at night."