To test the effect of a new exercise routine on muscle growth, a researcher sets up the following experiment: 60
volunteers subjects (40 men and 20 women) of average
build are selected to participate in the study. Their body
mass and muscle sizes (biceps, thighs, etc.) are
measured. The researcher gives all the men a DVD with
the new exercise routine, and the women a DVD with a
standard routine, but only the researcher knows this.
The results of the experiment are likely to be invalid mostly
because
the subjects did not know if they were getting the
real treatment.
the gender of the patient is a confounding variable
in this experiment
the treatment group and control group were not the
same size.
the subjects were volunteers.
None of the above

explanation:

a fuel engine ( known as a gasoline engine in american english )is an internal combustion engine with spark ignition, designed to run on petrol (gasoline) and similar volatile fuels.

correct it is c.) b b

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle  

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.