grammatical error

[siruss]

This question is about finding a grammatical error.
There are four sentences, one of which has an error.
Please, help me.

A: Something has to be done about the economy.
B:I know. I read the statistics in the newspaper this morning.
A:What do you think is causing all the problems?
B:They may due to the high oil prices and the lack of jobs.


The answer key says the answer is the fourth sentence.
Can you tell me why?


One more question.
What is the most proper word to fit in the blank?
A: Look at the way Susan is overdressed!
B:Isn't that a bit too ______ for the occasion?
a) proud b_ showy c) loud d)cozy

I thought the answer was c) loud.
But the answer key says the answer is b)
Can you tell me why?

[Casiopea]

I'll help you with the second one.

A: Look at the way Susan is overdressed!
B: Isn't that a bit too ______ for the occasion?

a) proud
b) showy
c) loud
d) cozy

overdressed, dress oneself more formally or elaborately than appropriate or desirable.

showy, elaborate

[siruss]

I'll help you with the second one.

A: Look at the way Susan is overdressed!
B: Isn't that a bit too ______ for the occasion?

a) proud
b) showy
c) loud
d) cozy

overdressed, dress oneself more formally or elaborately than appropriate or desirable.

showy, elaborate

Thank you so much!It's a great help to me.

[mochimochi]

They may be due to the high oil prices and the lack of jobs.

Due is an adjective, so be is needed.