1. When you phoned, I a shower. *
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This is a question or what sorry I don't understand this???

When you phoned me I was having a shower.

Using dark print on a light background best demonstrates the design principle of contrast.

In a very basic definition, contrast is the degree of difference between two elements of your design.

Contrast has a great effect on readability and legibility as well, while low contrast not only reduces the difference between elements, it also decreases readability.