It had been difficult, because of the unrest.
Modeling of these defects has been difficult because of the challenges associated with engineering mtDNA.
"It has been difficult because of the domination of the English, but we are making progress.
Cooperation among the exchanges has also been difficult because of their fierce competition.
However applying the results from one institution to another has been difficult because of the variations in imaging techniques and feature measurement.
Interpretation of these trials has been difficult because of multiple variables, which include differences in trial design, cell type, timing of cell delivery, and outcome measurements.
However, unraveling the mechanisms underlying brain aging, AD and impaired function has been difficult because of the complexity of the networks that drive these aging-related changes.
Efforts to modulate the biological activity by structural modifications using synthetic organic chemistry have been difficult because of the complexity of its chemical structure.
Tillery said saving for a down payment has been difficult because of her nonprofit salary, rent that rises almost every year and her student loan payments.
All the C.E.O.'s I've talked to recently have said that the last year has been difficult because of the economy, but they've learned about themselves as leaders.
I don't regret the life-altering work I've done on the Lincoln script, but everything has been difficult because of Lincoln".
