Spot the errors

It's clearly your homework. What's your result?

I want the answers to above question because I want to clear my concepts .its not my homework. if somebody knows it please give the answer.please let me know the answers.

1) The dreg of the Ganga river / were also affected / by the beating / in irregular way. / No error
What is a "dreg"? What is this sentence supposed to mean?

2. The earthquake / is a natural phenomena / and it is / beyond human control. / No error
An earthquake; use the singular 'phenomenon'

3. The customer / handed over / a five hundred-rupees note / to the shopkeeper. / No error
a five-hundred-rupee note

4. The class teacher / gave her home works / and instructed her to do it / in the morning. / No error
homework

5. Dr. C. K. Narayan declared that / Ramu’s intestine was / not working properly and so he needed / medical treatment for a long time. / No error
No error if both diagnosis and treatment are in the past.

6. Shobhana does her best / but she does not understand why she / does not get expected / mark in the examination. / No error
the marks she expects?

7. They will not / be allowed / to go / to play outdoor games. / No error
Omit 'to go'.

8. Mr. Thakur said / that he had never seen / such a lovely spectacles / in his life. / No error
Spectacle

9. Her first offspring / could not survive / but her other two offsprings / are alive till now. / No error
omit 'offsprings". That word, in any case, does not have a plural.

10. I know / that / he has three issues / two daughters and a son. / No error
Replace 'issue' with 'children'.

11. The surrounding / of this museum / attracts a large number of people / coming from the other places. / No error
Surroundings; attract; from other places

1) The dreg of the Ganga river / were also affected / by the beating / in irregular way. / No error
What is a "dreg"? What is this sentence supposed to mean?

------dreg means residue, this sentence means residues can be removed by beating it an irregular way...so what can be the error in the sentence?
is " the" before dreg a correct usage? or there is any other error?




5. Dr. C. K. Narayan declared that / Ramu’s intestine was / not working properly and so he needed / medical treatment for a long time. / No error
No error if both diagnosis and treatment are in the past.
--- here he means ramu but ramu is not mention in the sentence so that part be the error???



7. They will not / be allowed / to go / to play outdoor games. / No error
Omit 'to go'.
why there is a need o omit "to go"??