几道SAT语法题不懂 请赐教～1 Quincy took Dan to Derek's home (for a visi

几道SAT语法题不懂 请赐教～
1 Quincy took Dan to Derek's home (for a visit),(never imagining) that five years (would pass) before (seeing) Derek again.
为什么seeing错了呢?
2No one (but) a fool would (readily) lend money to a person who (is known) (to be) a frequent gambler.(No error)
这 题为什么no error 既然前面是would 后面的is 不用was吗 什么时侯would可以这样用?
3Despite research (on the diagnosis) of heart disease and the use of (increasingly) sophisticated technology (in its treatment),the condition of coronary arteries (is) still difficult to assess precisely.No error
这题为什么是no error in its treatment里面的its不会指代不清吗 前面既有heart diseas 还有technology
4Almost all drugs go through strict testing before approval and failing at least once.
A (as it is now)
B approval,failing
C approval; failure occurring
D approval; they failed
E approval but they have failed
这题我选的D 答案应该是B 请问为什么?