Why is assessment important?

Option D - When Yoshiro saw the beautiful cabin by the lake, he was happy.
A is wrong because a semicolon (;) is use to separate major sentence elements. This is a continuing sentence, no need for a semicolon.
B - no need for a comma (,) after beautiful
C - I do not think there is a need for a comma after 'cabin'.

When Yoshiro saw the beautiful cabin by the lake, he was happy too.