Why was the iron gate a problem, and how was it solved?

The daube has narrowed, workers dug a canal there, and larger ships could not travel farther than that point

Explanation:

The fashion of Iron Gate was changed, but the hinges did not change in a way. Even though the matter would have been made to look like rehung used in making bore marks on the tools that did not exist in the past years. The houses were made of shell, however because of the inconsistency; Mac suggested the establishment of iron gates to replace the traditional ones.

i'm sure the answer you are looking for would be

a. an ice age

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