What part of this sentence is grammatically incorrect? they were so engaged with each others thinking that they exchanged email addresses after the conference.

Lots of elementary school kids play sports after school. they play soccer, tennis, football, baseball, and even lacrosse. but i think that another great way to spend the afternoon is by playing a non-physical activity: chess. at our school we have a chess club that meets every week to play games and to learn about chess-related issues. chess is a wonderful game for many reasons. chess teaches students to be patient and not rush decisions. chess also teaches students how to strategize their future plans. and finally, chess teaches students the importance and necessity of sacrifice. chess can teach students just as much as any other sport. which sentence could best be added to this paragraph as a supporting detail? a) chess is not as fun as playing a sport outdoors might be. b) my father is very good at chess and plays a game with me every night. c) chess teaches students to think ahead about the consequences of their actions. d) other activities that are as fun as chess are painting, drawing, dancing, and acting.