左挑右选is a chinese idiom.左means left .右means right .in this sentence "左-右-"is a form of chinese idiom.there are lots of idioms like 左挑右选,such as 左拥右抱，左思右想 and so on.
挑and选 ,both means select or choose ..左挑右选means when you have many choices ,you need to think twice and select the best one.
摘 and 掰 both means pick. The difference between them is that when you use the strength of your fingertips ,it's called 摘.When you use the strength of your wrist ,it's called 掰.
扔 means throw or discard. 丢 has two meanings,means throw or drop ,and it also means lose.
in this sentence ,扔 and 丢 both means throw.
便 has lots of use,here it is a preposition,means then.
他便扔下玉米means "then he throwed the corn."
抱is a verb,means embrace or hold something with your arms .
怀抱is a noun,means chest or bosom.
怀抱can also be used as a verb ,and it has no difference with抱.
Here 怀is a noun,means chest. 抱is a verb. means carry them in arms.