Please help someone. Saturation divers who spend days or weeks under water often breathe a mixture of helium and oxygen. One side effect of this gas mixture is that it makes the divers' voices higher-pitched. What is the cause of this increase in pitch?
a. Sound waves travel slower in the helium-oxygen mixture, resulting in a higher frequency for the same wavelength.
b. The helium-oxygen mixture decreases the amplitude of the waves, which increases their frequency.
c. Ultraviolet, X-rays, gamma rays, and sound waves travel faster in the helium-oxygen mixture, resulting in a higher frequency for the same wavelength.
d. The helium-oxygen mixture increases the amplitude of the waves, which increases their frequency.

The chart shows the costs and shipping times for materials that a company needs to build a new product. which describes the best trade-off if the company needs to start building their product within the next two years? they should order the domestic materials because it is always best to choose the fastest shipping time. they should order the imported materials because it is always best to choose the lowest cost for materials. since the shipping time is longer, they should order the domestic materials because the additional cost is worth it to get the materials in time. even though the shipping time is longer, they should order the imported materials because they are less expensive and should arrive in plenty of time to build the product.