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Answer:
 1. a, b, c - represent growth
 2. b, c, d - represent decay
Explanation:
If increasing x results in a larger value, the function represents growth. If it results in a smaller value, the function represents decay.
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To answer these questions, you can look at the base and the exponent. When we say "exponent" here, we mean the coefficient of the exponent variable. There are four possibilities:
 growth: 
- exponent positive, base > 1
 - exponent negative, base < 1
 
 decay:
- exponent positive, base < 1
 - exponent negative, base > 1
 
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Growth questions:
 1.77^x -- growth
 1.5^(x/2) -- growth
 0.5^(-x) -- growth (= 2^x)
 e^(-t) -- decay (e ≈ 2.718)
Decay questions:
 1.7^x -- growth
 1.7^(-2x) -- decay
 (1/3)^x -- decay (= 3^(-x))
 2^(-x) -- decay