A learner accidentally marks a page in a textbook that gives the definition of redshift. The mark hides the three key words 1, 2 and 3. Redshift is ......1...... in the observed ......2...... of electromagnetic radiation coming from ......3...... stars and galaxies. What are words 1, 2 and 3?
- A1: an increase; 2: frequency; 3: receding
- B1: a decrease; 2: frequency; 3: approaching
- C1: an increase; 2: wavelength; 3: receding
- D1: an increase; 2: wavelength; 3: approaching