Quickly Solve this riddle

7 - 4 + 3 * 0 + 1 = ?

You are an expert on paranormal activity and have been hired to locate a spirit haunting an old resort hotel. Strong signs indicate that the spirit lies behind one of four doors. The inscriptions on each door read as follows:

Door A: It's behind B or C
Door B: Its behind A or D
Door C: It's in here
Door D: It's not in here

Your psychic powers have told you three of the inscriptions are false, and one is true. Behind which door will you find the spirit?

I’m orange, I wear a green hat and I sound like a parrot. What am I?

When it's bad luck to meet a black cat?

A boy and a girl are sitting on the porch.
"I'm a boy," says the child with black hair.
"I'm a girl," says the child with red hair.
If at least one of them is lying, who is which?

I make a loud sound when I’m changing. When I do change, I get bigger but weigh less. What am I?

There was once a college that offered a class on probability applied to the real world. The class was relatively easy, but there was a catch. There were no homework assignments or tests, but there was a final exam that would have only one question on it. When everyone received the test paper it was a blank sheet of paper with a solitary question on it: 'What is the risk?'.Most students were able to pass, but only one student received 100% for the class! Even stranger was that he only wrote down one word!
What did he write?

How much will a 38° angle measure when looked at under a microscope that magnifies ten times?

I have no life, but I can die. What am I?

I am lying and I always lie. Tell me whether I am lying or telling the truth.