Hand in glove

In the following question choose the altranative which best hexpresses the meaning of the idiom /phrase

A hard nut to crack

(1)it being very dark (2)the visitors found it difficulty

(3)to locate the switch (4) no error

In the following question some parts of the sentance khave errors .Find out which has error .the number of that part is the answer .If a sentance has no error then the ankswer is (4)

Among the numbers given below which one is mono -digital:

REPEAL