7 Which of the following is WRONG for the PCA? (Choose the correct answer from next options (1)~(4):) (1)The length of the first principal component vector is larger than that of the second principal vector. (2)Any two principal components are orthogonal to each other. (3)PCA may be used for dimensionality reduction by keeping only a small number of principal components (4)The length of each principal component vector is equal to 1