Which one of the following is true for EM wave propagation through rectangular waveguide of cross-section 2a x a

• critical wavelength for TE10 mode is the same as that for TE02 mode
• critical wavelength for TE10 mode is one half of that for TE10 mode
• critical wavelength for TE10 mode is the same as that for TM10 mode
• critical wavelength for TE10 mode is double that for TE01mode