Why did the researchers NOT tell the patients which pill they were given? A. to make sure they Did't get get angry.
B. to prevents errors in data collection.
C. to keep people from leaving the study.
D. to prevents bias in the data collection

acid rain does not usually kill trees directly. instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. the main atmospheric pollutants that affect trees are nitrates and sulphates.

answer:

technetium is the most reactive. this is followed by silver. the least reactive out of these three elements is strontium.

qualitative observation deals with data that can be observed with our senses: sight, smell, touch, taste, and hearing. they do not involve measurements or numbers. for instance, colors, shapes, and textures of objects are all qualitative observations.