Ответ:

# C

number = input('Ввод: ')

highest = 0

for i in number:

   if int(i) > int(highest):

       highest = i

print(highest)

# D

number = input('Ввод: ')

list_num = list(number)

for i in range(len(list_num) - 1):

   if list_num[i] == list_num[i + 1]:

       print('да')

       break

else:

   print('нет')