Which statement best describes a physical change ? a. changes can occur to certain chemical properties of the substance, but the overall shape of the substance will remain the same. b. changes can occur to certain physical properties of the substance, but the overall shape of the sub stance will remain the same. c. changes can occur to certain physical properties of the substance, but chemical composition of the substance will remain the same. d. changes can occur to certain chemical properties , but chemical composition of the substance will remain the same.

Consider each of the electric- and magnetic-field orientations given next. in each case, what is the direction of propagation of the wave? a)\vec ein the +xdirection,\vec bin the +ydirection. choose+ x direction- x direction+ y direction- y direction+ z direction- z direction b)\vec ein the -y direction,\vec bin the +x choose+ x direction- x direction+ y direction- y direction+ z direction- z direction c)\vec ein the +z direction,\vec bin the -x direction. choose+ x direction- x direction+ y direction- y direction+ z direction- z direction d)\vec ein the +y direction,\vec bin the -z direction. choose+ x direction- x direction+ y direction- y direction+ z direction- z direction