53. To determine how to crash activity times a. normal activity costs and costs under maximum crashing must be known. b. shortest times with crashing must be known. c. realize that new paths may become critical. d. All of the alternatives are true.

D. All of the alternatives are true.

Explanation:

Crash activity time are been used in the in different organisations for different reasons. In the case, above the mentioned conditions in all options are been put to consideration. Because in its determination, one has to analyze thoroughly its critical path method in its first step; here the tasks are been shortened before being tackled. Secondly, you identify the newer critical ways in dealing of the things.

Also, normal activity costs and costs under maximum crashing are been made known. Therefore, all options above appear to be one of the steps in critical ways of determining crash activity time.

ans.

heterothermic organisms include those organisms that can switch between homeothermic (having body temperature higher than environment) and poikilothermic (having variation in internal body temperature) strategies.

some migratory birds show heterothermy as they decrease their metabolic rate during cold nights to keep their body temperature low. drop in metabolic rate allows increase in production efficiency of birds that reduces the internal body temperature to make it equal to external cold temperature during cold nights.

thus, the correct answer is 'birds allow their temperature drop in order to increase their production efficiency.'

the first successful, urban blues recording, selling more than 75,000 copies, was made in year 1920.

mamie smith recorded the first commercially successful example of the urban blues,   with the recording of “crazy blues”."crazy blues" was recorded on august 10, 1920, in new york city. within a month of the release of “crazy blues” it had sold 75,000 copies.