we can 50/50 it cause i can see somebody writing a letter and sending it to a loved one but i can also see people calling and texting one another. But in answer b it says "Many people have cell phones and computers now". but it does not say people use them to communicate as to c it says "In the old days, people had to rely on letter writing".
“Based on previous studies, scientists estimated how much plankton the zebra mussels could filter out of the water. (Phytoplankton and zooplankton are microscopic organisms that are two critical components of the river's food web.) The numbers suggested the impact of zebra mussels on the river could be huge.”
