Do you know where mississippi river is? a) an b) the c) - he twenty in a month a) will be b) am going to be c) is we go to peru next year. we`re not sure. a) might b) should c) probably that`s the woman son is an actor. a) who b) whose c) which this afternoon, we sandboarding. a) are going b) are going c)will i`m bored camping trips. let`s go on a safari. a) from b) of c) for перед вами такое , похожее на викторину. ответы я знаю, поэтому в этом не заключается. тут вы должны проявить свои знания и написать, объяснить мне почему тут именно этот вариант ответа. это нужно, и объясняйте, , понятно. заранее всем !

Do you know where the Mississippi River is?
THE is the definite article.   when you have ONE of something that is definite, you use THE.  there is only one mississippi river, so you must use 'the'.

'an' is an indefinite article, not appropriate. if you have one of something thats not specific such as 'an apple'. 

He will be twenty in a month.
'in a month' says this is in the future, so you need a future tense verb
'am' goes with 'I' always  (I am ...)
'is' is present tense, but you could say 'he is going to be twenty in a month'

We might go to Peru next year.  We're not sure.
'not sure' means it may not happen. 'might' is also uncertain
so 'should' means we need to do something

that's the woman whose son is an actor.
i am not sure why, just that this one is correct

This afternoon, we are going sandboarding
a) and b) are the same answer
'this afternoon' means future tense
'going to' states a plan or intention, where 'will' is used in a different sense, as in a promise or request for help

i'm bored of camping trips.  let's go on a safari
'for' is definitely wrong
i have heard 'from' used, but i suspect it is not proper grammar

извините за все английский, мой руский не достаточно хорошо.