About activity float in networks: float can be positive, zero, or negative; positive float allows delay up to its value without delaying the project; negative float implies inevitable project delay unless recovered; zero float marks a critical activity—i.e., all the above.

Introduction / Context:
Float (slack) quantifies schedule flexibility. Understanding its sign and implications is central to critical path control and risk management.

Given Data / Assumptions:

• Activities have computed early/late times.
• Total float can be positive, zero, or negative based on constraints.
• Project finish target is fixed by management/contract.

Concept / Approach:
Total float = LS - ES = LF - EF. Positive float allows delay up to that amount without affecting project completion; zero float means the activity is on the critical path; negative float occurs when imposed dates are tighter than network logic permits, signaling required recovery (crashing, resequencing, or resource boost).

Step-by-Step Solution:
1) Compute ES, EF via forward pass; LS, LF via backward pass.2) Calculate total float: TF = LS - ES (or LF - EF).3) Interpret sign: TF > 0 → safe delay within TF; TF = 0 → critical; TF < 0 → schedule infeasible unless recovered.4) Conclude that all statements A–D correctly describe float behavior.

Verification / Alternative check:
Imposed finish milestones can drive negative float; mitigation by crashing reduces durations to restore TF to zero or positive values.

Why Other Options Are Wrong:

• Any single statement (A–D) is true but incomplete; the inclusive option states the full picture.

Common Pitfalls:

• Assuming negative float is an error rather than a warning of infeasibility.
• Using up positive float unintentionally through slow approvals.

Final Answer:
All the above.